UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


THE  GIFT  OF 

MAY  TREAT  MORRISON 

IN  MEMORY  OF 

ALEXANDER  F  MORRISON 


The  RALPH  D.  REED  LIBRARY 

•o 

DEPARTMENT  OF  GEOLOGY 

UNIVERSITY  OF  CALIFORNIA 

LOS  ANGELES,  CALIF. 


PREFACE. 


IN  writing  this  volume  I  have  not  had  any  intention  of  attempt- 
ing to  add  another  to  the  text-books  of  geology  in  the  English 
language.  Of  these  there  is  already  an  ample  supply.  Sir  A. 
Geikie's  "Text-book  of  Geology,"  Professor  Prestwich's  "Geology," 
and  the  edition  of  Phillips'  "Manual  of  Geology"  by  Professor  H. 
G.  Seeley  and  Mr.  R.  Etheridge  leave  no  gap  to  be  filled  among 
works  of  larger  size,  while  a  student  not  yet  ripe  for  these  has 
ample  choice  among  books  on  smaller  scale,  which  can  be  arranged 
in  a  graduated  series  from  Mr.  Jukes-Browne's  "Handbook"  to  the 
most  elementary  "Primer." 

So   I    have    not  endeavored  to  write  a  book  which  is  designed 
to   prepare  for  an    examination    or   to   serve   as   a   guide   to    the 
N     literature  of  the  subject.    A  class  of  persons,  however,   still  exists 
ai     to  whom    I  hope    this    volume    may   be    acceptable   and    useful. 
Many   who,  to   use    the   common    phrase,    have  received   a  good 
21    education,   though  they  feel  much   interest  in  the  history  of  the 
^    earth   on  which   they  live,  have  neither  the  leisure  nor  the  incli- 
•    nation   to   master  the  technicalities  or  to  enter  into  the  minute 
J    details  of  any  one  branch  of  science.     At  the  present  time  there  is, 
^     I  think,  a  real  danger  lest  such  persons  should  be  repelled  from  all 
«c    knowledge  of  science  by  its  increasing  complexity.     To  speak  of 
<yj    geology  only:  Forty  years  since  a  book  dealing  with  the  main  prin- 
2     ciples  of  geology,  such  as  Sir  C.  Lyell's  well-known  work,  would 
£     have  been  understood   with  little  difficulty  by  any  man  of  good 
£     general  education  :  two  pages  of  print  would  have  contained  all  the 
5     technical  terms  which  had  to  be  mastered.     But  these  have  now 
become  so  numerous  that  the  beginner  has  not  only  to  comprehend 
new  ideas,  but  also  to  learn  a  new  language.     To  some  extent  this 
is  inevitable.     As  science  increases  in  scope  and  complexity  tech- 
nical terms  become  more  necessary.     They  are  helpful  in  express- 
ing ideas  concisely  and    precisely ;   still  they  tend   inevitably  to 
diminish  the  number  of  those  who  take  an  interest  in  any  subject, 
and  to  restrict  all   study  of  it  to  those  who  make  it  a  profession. 
This  may  prove  ultimately  prejudicial  by  fostering  a  narrowness  in 

£31684 


iv  '  PREFACE. 

its  votaries,  both  of  views  and  of  sympathies.  No  doubt  the  judg- 
ment of  experts  is  less  fallible  than  vox populi ;  but  experts  some- 
times suffer  from  an  hypertrophy  of  learning  and  an  atrophy  of 
common  sense  to  which  men  of  wider  outlook  and  more  general 
culture  can  apply  a  wholesome  correction.  Technical  terms  also, 
as  I  venture  to  think,  are  sometimes  coined  without  good  cause. 
The  use  of  them  seems  to  be  pleasing  to  some  minds,  for  it  indi- 
cates an  initiation  in  mysteries  and  a  superiority  to  the  common 
herd.  But  from  a  terminology  not  generally  intelligible  worse 
evils  than  the  gratification  of  personal  vanity  are  apt  to  arise — 
namely,  the  worship  of  phrases  and  the  substitution  of  words  for 
ideas.  Science,  as  it  grows,  suffers  from  its  epidemics,  and  high- 
sounding  words  are  often  the  bacteria  which  communicate  disease 
to  mental  constitutions  of  the  less  vigorous  type.  To  some  per- 
sons a  sonorous  term  seems  to  be  so  satisfactory  that  it  passes 
current  for  an  idea,  and  is  a  mask  for  any  amount  of  hazy  indefi- 
niteness.  We  are  oft'en  told  that  plain  living  and  high  thinking  go 
together  in  the  daily  life;  may  it  not  be  that  plain  speech  and 
accurate  thought  are  not  so  far  apart  in  science?  An  English 
phrase  may  require,  when  printed,  a  few  more  letters  than  a  misbe- 
gotten compound  of  Greek  words  (often  barbarous  to  the  ears  of  a 
scholar) ;  but  it  possesses  this  advantage,  that  he  who  runs  may 
read,  and  he  who  speaks  cannot  clothe  himself  with  grandiloquence 
as  with  a  cloak,  and  conceal  mental  poverty  beneath  verbal  splendor. 
So,  though  technical  terms  cannot  be  wholly  avoided,  and  the 
scientific  names  of  plants  and  animals,  as  a  rule,  must  be  employed 
for  the  sake  of  precision,  I  have  striven,  as  far  as  possible,  to 
abstain  from  them,  and  to  write  as  addressing  men  and  women  of 
good  general  education  who  might  desire  to  know  something  of 
the  methods  of  reasoning  which  are  adopted  in  geology,  and  of  the 
general  conclusions  to  which  these  have  led.  But  in  trying  to  tell 
"the  story  of  our  planet"  in  fairly  plain  words  I  have  not  shrunk 
from  dealing  with  some  of  the  more  difficult  questions  which  it 
involves.  In  short,  the  plan  on  which  this  book  has  been  framed  is 
generally  similar  to  that  adopted  by  Sir  C.  Lyell  in  his  great  work 
"The  Principles  of  Geology."  But  as  it  is  now  twenty-one  years 
since  the  last  edition  of  "The  Principles"  was  published,  and  the 
representatives  of  its  author,  doubtless  through  reverence  for  his 
memory,  have  not  attempted  to  revise  or  alter  a  work  which  is 
rightly  numbered  among  our  classics,  there  is,  I  believe,  room  for  a 
book  which  covers  somewhat  the  same  ground. 


PREFACE.  V 

Still  I  have  not  adhered  at  all  closely  to  the  lines  followed  by 
Sir  C.  Lyell,  because  at  the  time  when  he  wrote  many  things  had 
to  be  fully  demonstrated  which  now  (thanks  largely  to  him)  may 
be  taken  almost  for  granted.  In  some  instances,  however,  I  have 
ventured  to  draw  upon  the  materials  collected  by  him,  and  have 
freely  used  throughout  this  book  such  facts  as  may  be  called  the 
common  property  of  all  teachers  of  geology  without  deeming  it 
necessary  always  to  indicate  the  source  from  which  they  were 
derived.  As  a  rule,  I  have  only  inserted  references  where  the 
actual  words  of  an  author  have  been  quoted;  since,  as  already 
stated,  this  is  not  meant  to  be  a  text-book.  It  is  founded  on  a 
part  of  my  lecture  notes,  and,  as  everyone  knows  who  has  taught 
for  a  good  many  years,  ideas  borrowed  from  books,  picked  up  in 
conversation,  and  originated  in  one's  own  brain,  get  at  last  hope- 
lessly mixed  up  together  in  a  kind  of  mental  conglomerate.  Not 
seldom  also  a  teacher  recognizes  in  the  writings  of  a  former  pupil  a 
flower  the  seed  of  which  was  sown  in  his  own  lecture  room.  Of 
this  he  cannot  complain,  for  it  is  one  of  his  highest  rewards.  A 
teacher  does  not  and  should  not  claim  any  copyright  in  his 
thoughts:  he  is  doing  his  duty  best  when  he  drops  each  conception 
of  his  own  mind,  as  it  is  duly  ripened,  into  the  receptive  mental 
soil  of  his  abler  students,  there  to  germinate  and  bear  fruit,  perhaps 
better  than  on  the  exhausted  arable  field  of  his  own  weary  brain. 
So  I  may  be  sometimes  suspected  of  plagiary  when  it  is  really 
from  myself;  and  if  in  these  pages  any  geologist  recognizes  ideas 
of  his  own,  used  without  acknowledgment,  I  crave  his  pardon,  and 
trust  to  the  liberality  of  true  men  of  science.  We  borrow  and  we 
give :  "  Hanc  veniain  petimnsque  dcimusque  vicissiin" 

It  may  be  well  to  observe  that  I  have  excluded  from  this  book 
a  few  topics  on  the  ground  of  their  being  either  too  technical  to  be 
made  intelligible  to  the  general  reader  or  at  present  too  uncertain 
in  their  bearing  on  the  subject  to  be  of  any  real  service  to  him. 
As  a  rule,  I  have  confined  myself  to  the  more  important  questions 
(as  they  seemed  to  me),  and  have  set  forth  the  views  which  are  the 
more  generally  entertained.  Still  I  have  not  thought  it  needful 
entirely  to  sink  my  own  individuality,  and  on  one  or  two  points 
have  expressed  opinions  which,  just  at  the  present  time,  are  those 
of  the  minority  (though  a  large  one)  rather  than  of  the  majority  of 
geologists.  As  my  excuse  for  so  doing,  I  must  plead  that  these 
questions  for  many  years  have  been  to  me  subjects  of  special 
study,  and  that  in  regard  to  them  I  have  had  rather  exceptional 


vi  PREFACE. 

opportunities  of  forming  an  opinion.  Chief  of  these  are — the 
physical  geography  of  Britain  in  the  earlier  part  of  the  Triassic 
period,  the  effects  and  former  extent  of  glaciers,  and  the  history 
and  age  of  certain  crystalline  rocks.  The  last  question,  which  is 
one  of  great  interest  and  far-reaching  importance,  practically  indi- 
cates my  position  in  regard  to  the  "Uniformitarian  creed"  in  geol- 
ogy, and  the  one  matter  on  which  a  slight  difference  in  opinion 
from  the  revered  author  of  "The  Principles"  will  be  perceptible. 
To  "Catastrophical  geology"  I  am  no  less  opposed  than  were  our 
great  masters  Hutton  and  Lyell.  I  fully  accept  the  leading  prin- 
ciples of  Uniformitarian  geology,  but  I  cannot  close  my  ears  to  the 
conclusions  of  men  eminent  in  experimental  and  mathematical 
physics,  or  insist  on  regarding  "the  universe  as  a  self-winding 
clock."  Nay,  I  venture  to  think  that  even  in  the  earth  itself  we 
can  discover,  by  processes  strictly  inductive,  some  sign  of  its  begin- 
ning and  some  foreshadowing  of  its  end. 

I  hope  that  no  serious  errors  are  lurking  in  these  pages;  but 
geology  has  now  become  so  vast  a  subject  that  perfection  in  all  its 
branches  would  almost  be  another  name  for  scientific  omniscience; 
and  nothing  makes  one  so  conscious  of  the  truth  of  the  saying, 
Humanum  est  errare,  as  writing  a  book.  Besides  the  errors  due  to 
the  author's  own  ignorance  or  to  the  unaccountable  freaks  and  per- 
versities of  his  memory,  there  are  those  typographical  mistakes 
which  so  often  contrive  to  elude  his  notice  as  to  tempt  him  to 
believe  that  beings  not  wholly  beneficent  haunt  the  precincts  of 
the  printing  office.  If  errors  prove  to  be  few  in  number,  this  is 
largely  due  to  the  kind  assistance  which  I  have  received  in  the 
revision  of  the  proofs  from  Miss  C.  A.  Raisin,  B.  Sc.,  a  former 
pupil  and  now  frequent  helper  in  scientific  work,  to  whom  I  tender 
my  most  grateful  thanks.  These  also  are  due  to  the  authors, 
scientific  societies,  and  publishers,  hereafter  more  particularly 
enumerated,  who  have  permitted  the  use  of  illustrations  which 
were  their  property. 

The  study  of  geology  has  added  much  to  the  happiness  of  my 
own  life;  it  has  taught  me  to  appreciate  more  fully  the  beauties 
and  the  marvels  of  Nature;  it  has  often  restored  me,  when  weary 
and  jaded,  to  bodily  health ;  it  has  helped  me  in  bearing  those 
trials  which  are  the  common  lot;  if,  then,  this  book  is  so  fortunate 
as  to  interest  others  in  the  subject,  I  shall  count  that  a  high  reward. 

T.  G.  BONNEY. 

UNIVERSITY  COLLEGE,  LONDON,  1893. 


CONTENTS. 


PART    I. 

THE  STORY  :  ITS  BOOKS  AND  THEIR  SPEECH. 

CHAPTER  PAGE 

I.     INTRODUCTORY, 3 

II.     THE  LAND  REGION, 12 

III.  THE  AIR  REGION, 26 

IV.  THE  WATER  REGION, 50 

PART  II. 
THE  PROCESSES  OF  SCULPTURE  AND  MOLDING. 

I.     THE  WORK  OF  THE  ATMOSPHERE, 83 

II.     RAIN  AND  RIVERS  AS  SCULPTORS, 93 

III.  RIVERS  AS  TRANSPORTERS, ,        .        .116 

IV.  ICE  AS  SCULPTOR,          ». 129 

V.     ICE  AS  A  CARRIER,             142 

VI.     THE  WORK  OF  THE  OCEAN — MARRING  AND  MAKING,           .        .        .  152 

VII.     THE  PROLETARIAT  OF  NATURE,          ........  172 

PART  III. 
CHANGES  FROM  WITHIN. 

I.     MOVEMENTS  OF  THE  CRUST, .  199 

II.    VOLCANIC  ACTION  AND  ITS  EFFECTS,             220 

III.  EARTHQUAKES  AND  THEIR  EFFECTS, 262 

IV.  INTERNAL  CHANGES  IN  THE  EARTH'S  CRUST, 284 

PART   IV. 
THE  STORY  OF  PAST  AGES. 

I.     METEORS  AND  THE  EARTH'S  BEGINNING,           ......  297 

II.     THE  ERAS  AND  SUBDIVISIONS  IN  GEOLOGICAL  HISTORY,      .        .        .  318 

vii 


viii  CONTENTS. 

CHAPTER  PACK 

III.  THE  ARCHAEAN  ERA, .        .  335 

IV.  THE  BUILDING  OF  THE  BRITISH  ISLES, 354 

V.     THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS,       .        .        .        .404 

VI.    A  SKETCH  OF  THE  EARTH'S  LIFE-HISTORY, 430 

PART  V. 
ON  SOME  THEORETICAL  QUESTIONS. 

I.     THE  AGE  OF  THE  EARTH,          .        . 481 

II.     THE  PERMANENCE  OF  OCEAN  BASINS  AND  LAND  AREAS,      ...  486 

III.  CLIMATAL  CHANGE  :  ITS  CAUSE  AND  HISTORY, 491 

IV.  THE  DISTRIBUTION  AND  THE  DESCENT  OF  LIFE,          ....  508 


LIST  OF  ILLUSTRATIONS. 


FIG.  PAGE 

1.  Cardita  planicosta   (Upper    Eocene) ;   Melania   inquinata   (Lower   Eocene) ; 

Terebratula  semiglobosa  (Chalk),      ........  3 

2.  Chalk  of  Gravesend, 5 

3.  Sequence  of  Masses  of  Rock,  ..........  7 

4.  Comparative  Size  of  the  Sun  and  the  Earth, 10 

5.  The  Alps,  from  Berne, 14 

6.  A  Volcanic  Hill  (Vesuvius,  from  the  Sea) 16 

7.  Land  Hemisphere,  .          .         .         .          .         .         .         .         .         .         .17 

8.  Ocean  Hemisphere,     ...........  18 

9.  Block  of  Pudding  Stone, 20 

10.  Stratified  Rocks,           .         •. 21 

11.  A  Case  of  False  Bedding, 22 

12.  Joints   Exhibited   in   a   Mountain    Ruin,   from    the    Dolomites     of    Cortina, 

S.E.  Tyrol,          .                   23 

13.  Columnar  Jointing, 24 

14.  Columnar  Basalt,  Fingal's  Cave, 25 

15.  Diagram  of  Air  Currents  and  Atmospheric  Circulation,     .....  32 

1 6.  Chart  of  a  Cyclonic  Disturbance  over  the  British  Isles 36 

17.  A  Tornado,  from  a  Photograph, 40 

1 8.  The  Course  of  a  Tornado  in  the  West  Indies,  1868, 42 

19.  Map  of  Northwestern  Europe,  with  the  Submarine  Contours,  53 

20.  The  Attraction  of  the  Moon  in  Producing  Tides, 59 

21.  Diagram  Representing  Currents  in  the  Ocean, .62 

22.  Direction  of  Currents  to  and  from  the  Arctic  Ocean, 65 

23.  Snow  Crystals, 69 

24.  Terminal  Ice  Cave  and  Birthplace  of  a  River, 72 

25.  Crevasses  in  a  Glacier, 77 

26.  Diagram  Showing  the  Rate  of  Movement  in  a  Glacier,          .         x         .         .  78 

27.  Wind-worn  Rocks,  Yellowstone  Park 86 

28.  Diagram  Showing  the  Formation  of  a  Dune,         ......  87 

29.  Blown  Sand  advancing  on  Cultivated  Land,  Bermuda, 88 

30.  Tower  of  Eccles  Church,  A.  D.  1839, 89 

31.  Tower  of  Eccles  Church,  November,  A.  D.  1862,     .         .         .                 H'         .  90 

32.  A  Granite  Tor  on  Dartmoor, 96 

33.  A  Sand  Pipe, 97 

34.  Fossil  Rain  Prints, .         .         .         .  99 

35.  Earth  Pillars  on  the  Rittnerhorn%             .         ...         .         .         .         .  100 

36.  Section  of  Glen  with  Earth  Pillars .  101 

37.  A  Waterfall,  .         .         .         .         .  .         .         ...         .         .106 

38.  Diagram  of  a  Cirque,  Surenen  Pass,     .         ...         .         »         ..        .         •  107 

ix 


X  LIST  OF  ILLUSTRATIONS. 

FIG.  PAGE 

39.  Terraced  Cliff, •        •        •        •         .108 

40.  Gorge  in  Sloping  Beds 108 

41.  The  Gorge  of  the  Tamina,  Pfafers,  Switzerland 109 

42.  In  the  Bed  of  a  Canon,         ....                                                     .  in 

43.  Diagram  of  Course  of  a  River,  .         .         .112 

44.  Diagram  of  Winding  River,        .  113 

45.  Geyser  and  Mound  of  Silica,                                                                               .         .  n? 

46.  Terraces  at  Rotomahana, ^         .         .  119 

47.  Map  of  Volcanic  District,  Rotomahana,                                                                  .  121 

48.  Sketch  Map  Showing  Former  Extent  of  Alpine  Glaciers  (N.  Side),               „  .  132 

49.  Bird's-eye  View  of  Potholes  in  Glacier  Garden,  Lucerne,  .         .         .134 

50.  Roches  Moutonnfrs—The  Grimsel, 135 

51.  Map  of  the  Great  Lakes  of  Canada  and  the  United  States,        .         .         .         .  139 

52.  Glacier  with  Moraine  (Mer  de  Glace) 143 

53.  Glacier  Tables, 145 

54.  A  Perched  Block, 146 

55.  On  a  Greenland  Ice  Sheet,       .         .         . 148 

56.  The  Formation  of  an  Iceberg,      .........  149 

57.  Icebergs  Floating  out  to  Sea, 150 

58.  Ice- worn  Headland  in  Fjord,  near  Laurvik,  Norway, 155 

59.  Ice-worn  Rock  Torn  by  Waves,  near  Langesund,  Norway,        ....  156 

60.  Waves  Breaking  on  the  Beach .         .         .  157 

61.  Old  Harry  Rocks,  near  Swanage,     .         .         .   '     .         .         .  .      .         .         .159 

62.  Gulleys  in  Place  of  Dykes,  Strathaird,  Skye, 160 

63.  The  Frying  Pan,  Cadgwith,  looking  Seaward, 162 

64.  Inland  Cliff  and  Old  Sea  Bed,  West  Coast  of  Scotland,         ....  164 

65.  Insolated  Rocks  near  the  Lizard, 166 

66.  Shoals  and  Channels  at  the  Mouth  of  the  Thames,       ....  167 

67.  The  Mississippi  Delta,             170 

68.  Bird's-eye  View  of  the  Nile  Delta,  looking  Southward,        .      ,.         .         .  171 

69.  Concretions,  .         .   ^    .         .        .        .    -     .        .         .         .         .         .175 

70.  Thin  Slice  of  Shale  from  Kettle  Point,  Lake  Huron,            .         .         .         .  180 

71.  A  Living  Foraminifer  (Afiliola\      .         .  •       .         .         .         .         .         .         .181 

72.  A  Living  Chambered  Foraminifer  (Pulvinulina) 182 

73.  The  Shell  of  a  Globigerina,  .        ...        '.         .         .        .         .183 

74.  Coccoliths  and  Coccospheres, 184 

75.  A  Radiolarian  (f/aliomma), 185 

76.  Holtenia  carpenteri, 186 

77.  Glauconitic  Cast  of  a  Chambered  Foraminifer,  Showing  the  Passages  between 

the  Chambers,           ...........  187 

78.  Masamarhu  Island,  Map  and  Section,           .        „ 193 

79.  Masamarhu  Island,  Section,           '  .                  .        '        ,         .         .         .         .  194 

80.  Limestone  with  Crinoid  Stems,            .         . 196 

81.  Nummulitic  Limestone,            . 196 

82.  Columns  in  the  "  Temple  of  Serapis," 200 

83.  The  Temple  of  Serapis  at  the  Time  of  Deepest  Submergence,          .         .         .  202 

84.  Terraces  Cut  by  the  Sea,  Malanger  Fjord,  Norway 205 

85.  Sea-cut  Grooves  in  Smoothed  Rock,  N.  of  Alien  Fjord,  Norway,      .         .          .  206 

86.  Diagram  of  a  Fault,    . .  209 

87.  Diagram  of  a  Reversed  Fault, 209 


LIST  OF  ILLUSTRATIONS.  XI 

FIG.  PAGE 

88.  Flexures  in  Bedded  Limestone,  Draughton,  near  Skipton 210 

89.  Diagram  of  Folds  in  Stratified  Rocks,         .         .         .         .         ,-.         .  211 

90.  Diagram  of  Faults  in  Stratified  Rocks, 212 

91.  Folded  Strata  (Lower  Tertiary)  in  the  Hausstock,       .         ....         .  213 

92.  Process  of  Conversion  of  a  Fold  through  an  Overfold  into  an  Overthrust  Fault,  214 

93.  Section  across  the  Alps  in  the  General  Direction  of  the  St.  Gothard  Road,     .  215 

94.  Diagram  Illustrating  Professor  Favre's  Experiment, 216 

95.  An  Ejected  Clot  of  Lava,           .                  .         ...         .         .         .  221 

96.  Mud  Volcanoes,  Turbaco,  Colombia,                ; 222 

97.  Monte  Nuovo,  from  the  Seashore,      ........  223 

98.  Hawaii,  with  the  Craters  and  Lava  Streams  of  Various  Eruptions,           .          .  225 

99.  Map  of  Krakatoa,  before  the  Eruption  of  1883, 227 

loo.  Section  of  Krakatoa,  before  the  Eruption  of  1883, 229 

lor.  Section  of  Krakatoa,  after  the  Eruption  of  1883, 230 

102.  Cotopaxi,  from  San  Rosario  (10,356  ft.), 233 

103.  Dust  Cloud  from  Cotopaxi, 235 

104.  Vesuvius,  from  the  Bay  of  Naples, 236 

105.  Outline  of  Monte  Somma, 237 

106.  Breached  Craters,  Auvergne, 245 

107.  Section  of  the  Great  Geyser, 251 

108.  Diagram  Illustrating   Mallet's  Theory  of  the  Direction  of    Movement  from 

an  Earthquake  Focus, 263 

109.  Diagram  of  Seismic  Circles, 264 

1 10.  Street  Houses  in  Charleston  Damaged  in  the  South  Carolina  Earthquake  of  1886,  268 
in.  Fissure  Produced  by  an  Earthquake,  Bella,  Calabria,           ....  270 

112.  Cathedral  of  Tito,  Calabria,  after  the  Earthquake  of  1857,      ....  274 

113.  Street  View  in  La  Polla,  after  the  Earthquake  of  1857 275 

1 14.  Earthquake  Map  of  the  World 279 

115.  Spheroids  Inside  a  Column,  Showing  Independence  of  these  and  the  Sides 

(Auvergne), 287 

116.  Spheroidal  Structure  in  a  Mass  of  Volcanic  Ash  (Burntisland),         .         .         .  287 

117.  Cheese  Grotto,  near  Bertrich  Baden, 288 

118.  Surface  of  the  Sun,  as  Shown  by  a  Solar  Spot,        .         .                   ...  301 

119.  The  Annular  Nebula  in  Lyra, 303 

120.  Some  of  the  Latest  Fossils  (from  the  Scottish  Glacial  Clays),           .         .         .  320 

121.  A  Group  of  Crystals  (Quartz) 321 

122.  Palaeolithic  Flint  Implements,  from  St.  Acheul,  near  Amiens,         .         .         .322 

123.  Rocks    (Quadersandstein) :    Marterstelle,   from    the   Basteibrucke   in   Saxon 

Switzerland,1  Contemporaneous  with  the  Chalk  of  England,           .         .  323 

124.  Unconformity:  Upper  Old  Red  Sandstone  Resting  on  Silurian,      .         .         .  327 

125.  Loch  Maree — among  the  "  Foundation  Stones"  of  Scotland,       .         .         .  337 

126.  Ben  Slioch— a  Mountain  of  Torridon  Sandstone fci  .         .338 

127.  Polished  Slab  of  Eozoon  Canadense,            .         .         .         ...         .         .  345 

128.  Structure  of  Eozoon  Canadense,      . 346 

129.  Diagrammatic  Section  of  Eozoon  Canadense,       .         ...         .         .  347 

130.  Vertical  Section  of  a  Nummulite,            348 

131.  Diagram  of  Rock  at  Cote  St.  Pierre,           .         .         ...         .         .         .  349 

132.  A  Lower  Cambrian  Trilobite  (Paradoxides), 356 

133.  Restoration  of  the  Geography  of  Britain  in  Early  Carboniferous  Times,        .  363 

134.  Restoration  of  the  Geography  of  Britain  in  Keuper  Times,     ....  369 


LIST  OF  ILLUSTRATIONS. 


135.  Sun  Cracks  and  Footprints,  Trias,  Hessberg 375 

136.  Map  of  Deep  Borings  in  the  Southeast  of  England, 380 

137.  Restoration  of  the  Geography  of  Britain  in  London  Clay  Times,         .         .          388 

138.  Section  of  the  Scuir  of  Eigg,  . 39° 

139.  Section  at  Lenham, 391 

140.  Section  of  Buried  River  Channel  in  Essex, 396 

141.  Section  of  Thames  Valley  at  Goring, 397 

142.  Map  Illustrating  how  a  Rise  of  600  feet  (100  fathoms)  would  unite  Great 

Britain  with  Ireland  and  the  British  Isles  with  the  Continent,  .         .     399 

143.  The  North  Downs  and  Weald  Valley,         .         .         ...         .         .          402 

144.  Basaltic  Plateaus  on  the  Coiron  in  the  Ardeche, 409 

145.  Septum  and  Sutures  of  Amrtwnites,  Ceratites,  and  Nautilus,        .         .         .          435 

146.  Catamites  cannaformis, 439 

147.  I.epidodendron  elegans, '    .  -       .         .          439 

148.  Sigillaria  lavigata,        .......•*..     44° 

149.  Restoration  of  Olenellus, 442 

150.  Structure  of  a  Graptolite, .        .        .         .     443 

151.  Haly sites  catenulatus 444 

152.  Eurypterus  remipes,      ...........     445 

153.  Ganoid  Fishes  (Old  Red  Sandstone)  .......          447 

154.  Devonian  and  Carboniferous  Fossils, .         .     448 

155.  Cypris, 450 

156.  Pentacrinus  briareus  (Extracrinus),       .         .         .         .         .         .         .         .     455 

157.  Apiocrinus  (Jurassic), 456 

158.  Shell  of  a  Trigoniaf .         -457 

159.  Skeletons  of  Ichthyosaurus  and  Plesiosaurus  (restored),      ....          459 

1 60.  Pterodactylus  brevirostris, .     463 

161.  Cretaceous  Fossils 465 

162.  Skeleton  of  Iguanodon,          ..........     467 

163.  Engraving  of  Mammoth,  from  the  Dordogne  Caves  (reduced),     .         .         .          475 

164.  Mean  Annual  Isotherms  of  the  Norwegian  Sea 492 

165.  Diagram  of  the  Course  of  the  Winter  Isotherms  in  the  Northern  Hemisphere,          493 

166.  Diagram  of  the  Course  of  the  Annual  Isotherms  in  the  Northern  Hemisphere,     494 

167.  Surface  Isotherms  of  the  Sea  in  January  and  February,      ....          496 

168.  Diagram  of  an  Elliptical  Orbit,      .......         .-        .     499 

169.  Map  Showing  how  the  deep  narrow  Strait  between  Bali  and  Lombok  sepa- 

rates the  Australasian  from  the  Indo-Malayan  Fauna,          .         .         .          513 

170.  Various  Forms  of  Feet,  Illustrating  Development  of  one  Digit  and  Abortion 

of  Others, •        ••«...     516 

NOTE. — The  publishers  desire  to  express  their  thanks  to  Mr.  Murray  for  his  kindness 
in  granting  them  permission  to  include  Figs.  30  and  31,  from  Lyell's  "  Principles  of  Geol- 
ogy "  ;  to  Messrs.  Macmillan  for  the  use  of  Fig.  75  from  "  The  Voyage  of  the  Challenger" 
and  for  Figs.  78  and  79,  from  Captain  Wharton's  paper  in  Nature  ;  to  Messrs.  Bell  &  Son 
for  the  use  of  Figs.  12,  24,  25,  and  41.  To  the  Royal  Society  they  are  indebted  for  the 
use  of  Figs.  99,  100,  and  101  ;  Mr.  Whymper  has  also  been  good  enough  to  lend  two 
blocks  (Figs.  102  and  103)  from  his  "  Travels  in  the  Great  Andes"  ;  and  to  the  Council 
of  the  Geological  Society  they  are  indebted  for  Figs.  38,  115,  116,  51  (Spencer),  136  and 
140  (Whitaker),  138  (Sir  A.  Geikie),  139  and  141  (Prestwich)  ;  while  for  permission  to 
include  Fig.  149  they  have  to  thank  the  editor  of  Natural  Science.  Figs.  12,  58,  59,  62, 
84,  85,  105,  124,  and  131  are  from  sketches  by  the  author. 


LIST  OF  PLATES. 


A   GLACIER— MER   DE  GLACE,  WITH  THE   GRANDES   JORASSES   IN  THE 

DISTANCE,  . Frontispiece. 

MAP  SHOWING  THE  CONTOURS  OF  THE  ATLANTIC  OCEAN,  .  .  To  face  p.  54 
MAP  SHOWING  THE  CONTOURS  OF  THE  PACIFIC  OCEAN,  .  .  ,  "  56 
BIRD'S-EYE  VIEW  OF  THE  CANONS  OF  COLORADO,  ....  "  112 

VAAGEKALLEN,     LOFOTEN    ISLANDS— THE    WORK    OF    WEATHER    AND 

GLACIER,  "         152 

A  LAVA  STREAM  FLOWING  INTO  A  LAKE,  HAWAII,  ...  "         242 


PART  I. 
THE  STORY  :    ITS  BOOKS  AND  THEIR  SPEECH. 


THE  STORY  OF  OUR  PLANET. 


CHAPTER  I. 

INTRODUCTORY. 


FIG.  i. — (i)  Cardita  planicosta  (Upper  Eocene);    (2)  Melanin  inquinata  ("Lower  Eocene); 
(3)  Terebratula  semiglobosa  (Chalk).     All  about  half  natural  size. 

THESE  drawings  represent  three  specimens,  taken  almost  hap- 
hazard, from  a  collection  of  fossils.  Each  of  them,  beyond  all 
doubt,  once  must  have  been  part  of  a  living  creature.  The  first 
was  dug  out  of  a  sandy  clay,  between  high-  and  low-water  mark,  at 
a  place  called  Bracklesham,  on  the  Sussex  coast.  What  of  that? 
it  may  be  asked ;  what  wonder  at  finding  a  seashell  in  such  a  posi- 
tion? This  only:  that  nothing  exactly  resembling  it  could  now  be 
discovered  alive  in  British  seas — or,  indeed,  in  any  other  seas.  Yet 
it  was  formerly  common  enough,  for  dozens  of  similar  specimens 
could  have  been  picked  up  where  it  was  lying.  But  more  than 
this :  many  other  shells  were  abundant  in  that  clay,  not  ^one  of 
which  is  now  to  be  found  in  British  waters.  Indeed,  we  notice  on 
closer  study  that  they  are  more  like  the  shells  which  come  from 
shores  much  nearer  to  the  equator  than  those  of  our  islands.  Evi- 
dently it  is  many  a  long  year  since  their  tenants  died.  Every  trace 
of  ornamental  coloring  has  disappeared;  all  the  specimens  have 
become  of  a  uniform  gray  tint.  They  have  lost  the  animal  matter 


4  THE   STORY  OF   OUR   PLANET. 

which  strengthens  the  shell  of  the  living  creature ;  all  are  more  or 
less  brittle — some  break  almost  at  a  touch.  So  it  seems  reasonable 
to  infer  that  since  these  mollusks  lived  and  died  the  climate  of 
Britain  has  greatly  altered. 

The  next  fossil  came  from  a  dark  bedded  mud  in  the  Thames 
valley,  which  also  was  crowded  with  various  kinds  of  shells,  all 
extinct  species,  all  bearing  more  resemblance  to  those  which  now 
inhabit  warmer  regions  than  Britain.  The  animals  which,  at  the 
present  day,  are  more  nearly  related  to  them  live  in  rivers,  espe- 
cially where  these  begin  to  broaden  out  into  estuaries.  So  far,  then, 
there  is  nothing  surprising  in  finding  such  fossils  in  the  valley  of 
the  Thames,  some  three  or  four  leagues  below  the  port  of  London. 
But  the  clay  in  which  they  were  lying  is  at  least  fifty  feet  above 
the  present  level  of  the  river,  and  was  evidently  deposited,  as  may 
be  seen  on  closer  examination,  by  a  broader  and  grander  stream 
than  now  glides  below  the  slopes  of  Richmond  Hill  and  under  the 
bridges  of  London.  The  first  specimen  indicated  a  change  in  the 
tenants  of  this  part  of  the  globe  and  suggested  a  change  in  climate. 
This  one  not  only  gives  confirmatory  evidence,  but  also  intimates 
that  the  physical  geography  of  the  district  must  have  been  con- 
siderably altered. 

Let  the  third -specimen  now  tell  its  tale.  Like  the  others,  it  does 
not  represent  any  creature  actually  living,  though  kindred  forms 
are  not  uncommon,  and  it  can  be  referred,  like  them,  to  a  well- 
known  genus.  All  three,  however,  are  best  represented,  and  may 
be  said  to  be  at  home,  in  distant  seas.  But  this  specimen  was 
obtained  in  a  pit  on  the  slopes  of  the  Downs,  some  five  hundred 
feet  above  the  present  sea  level.  Yet  more,  if  we  minutely 
examine  the  pure  white  chalk  in  which  this  shell  was  embedded,  if 
we  separate  it  carefully  particle  from  particle,  and  place  the  dust, 
properly  mounted,  under  a  microscope,  we  shall  find  that  not  a 
little  of  this  apparently  formless  powder  has  once  been  part  of  a 
living  organism,  which  can  be  often  identified  with  some  tiny 
creature,  a  tenant  of  the  open  ocean  far  away  from  shore.  So  this 
last  specimen  carries  us  yet  a  step  further  than  the  other  two. 
They  intimate  both  a  change  in  climate  and  geographical  condi- 
tions not  wholly  identical  with  the  present ;  this  tells  of  a  time 
when,  instead  of  a  green  sward,  dark  spotted  with  old  yew  trees, 
instead  of  trailing  hops  and  golden  corn,  a  waste  of  salt  waters 
extended  far  and  wide,  and  the  sea  lay  deep  where  now  the  Kentish 
Downs  overlook  the  Sussex  Weald. 


IN  TROD  UC  TOR  Y.  5 

Is  it,  however,  possible  to  find  any  other  explanation  of  the 
occurrence  of  these  shells  which  might  enable  us  to  avoid  conclu- 
sions so  startling?  At  first  men  were  content  to  regard  them  as 
freaks  of  Nature — mere  imitative  shapes,  like  the  "birds'  heads" 
and  other  "curiosities"  which  are  sometimes  brought  to  the  geolo- 
gist by  ignorant  folk  in  country  places.  But,  as  a  closer  study 
showed,  the  resemblance  was  too  perfect :  for  these  objects  copied 


FIG.  2. — CHALK  OF  GRAVESEND. 

Showing  foraminifera,  with  sponge  spicules.    (Much  magnified.) 


not  only  the  external  form,  but  also  the  internal  structure  of  shell 
or  of  bone;  and  it  became  clear  at  last  that  the  remains  of  the 
creatures  which  had  been  dead  but  a  few  years  or  centuries  could 
be  linked  on,  by  imperceptible  gradations,  to  those  which  were 
embedded  in  the  solid  rock,  and  had  been  subjected  tp  great 
mineral  change. 

By  some  persons  fossils  were  formerly  explained  as  the  results 
of  a  "plastic  force"  in  Nature ;  preliminary  and  abortive  efforts  to 
produce  the  more  perfect  form — very  much  as  when,  according  to 
Burns, 

Her  'prentice  ban'  she  tried  on  man, 
An'  then  she  made  the  lasses,  O  ! 


6  THE   STORY  OF  OUR  PLANET. 

But  such  an  explanation  obviously  was  no  better  than  a  mental 
stop-gap,  like  the  answers  with  which  parents  not  too  learned  try 
to  satisfy  inquisitive  children.  It  failed  to  content  men  who  wanted 
to  get  at  the  truth  of  things.  They  set  about  to  devise  a  more 
rational  account  of  this  strange  phenomenon.  Then  a  simple  way 
out  of  the  difficulty  seemed  to  present  itself.  They  believed  that, 
as  related  in  the  Hebrew  Scriptures  and  affirmed  by  the  traditions 
of  many  nations,  there  was  once  a  great  deluge,  when  the  whole 
world  was  overspread  by  water.  By  this  the  spoils  of  the  deep 
were  supposed  to  have  been  scattered  on  the  mountain  sides,  and 
thus  the  tale  of  the  flood  is  inscribed  on  the  records  of  the  rocks. 
For  a  while  this  explanation  seemed  satisfactory.  But  it,  too, 
has  been  tried  and  found  wanting.  Had  these  dead  and  gone 
organisms  been  found  only  on  the  surface  of  the  ground,  or  in  the 
mud  and  gravel  which  are  plastered  here  and  there  upon  the  hard 
rocks,  it  might  have  been  possible — though  there  would  have  been 
other  and  more  serious  difficulties— to  account  for  them  by  the 
surge  and  ebb  of  such  a  mass  of  water;  but  fossils  may  be  traced 
through  masses  of  rock  far  downward,  they  may  be  struck  in 
borings,  or  brought  up  from  shafts  at  depths  of  hundreds  of  feet 
below  the  surface.  A  more  extended  study  and  an  attempt  to 
classify  the  results  of  the  collector's  patient  searching  speedily  dis- 
close the  fact  that  particular  groups  of  fossils  are  characteristic  of 
certain  localities — that  they  are  not  huddled  together  pell-mell,  but 
occur  in  such  regular  association  that  if  one  or  two  well-known 
forms  are  picked  up  on  entering  a  quarry  it  can  be  predicted,  after 
a  little  experience,  what  is  likely  to  be  discovered  on  a  further 
search.  Another  generalization  soon  follows.  Different  kinds  of 
rock  are  seen  to  lie  one  upon  another,  like  a  number  of  volumes 
which  are  placed  either  flat  upon  the  table  or  resting  on  a  slope. 
It  is  observed  that  each  of  these  rock  beds  contains  a  different 
group  of  fossils:  each  volume  has  its  own  set  of  pictures,  telling 
the  tale  of  an  epoch  in  the  history  of  life.  When  the  scope  of  our 
observations  is  extended,  and  any  one  of  these  rock  masses  is 
traced  from  district  to  district,  as  it  appears  at  the  surface,  we  find 
that  although  some  changes  take  place  in  the  fossils  contained — 
just  as,  at  the  present  day,  differences  can  be  observed  in  the  vege- 
tation of  the  land  or  in  the  tenants  of  the  sea,  as  the  coasts  of  a 
continent  are  followed  from  east  to  west,  or  still  more  from  north 
to  south — nevertheless  the  rock  mass  can  be  identified  in  regions 
widely  separated.  As  in  the  annals  of  bygone  nations  connecting 


1NTRO&  UC  TOR  Y. 


links  are  found  by  which  the  historian  can  distinguish  correspond- 
ing epochs,  so  is  it  in  the  records  of  the  rocks,  when  the  tale  is  told 
by  these  "medals  of  creation,"  as  they  have  been  not  inaptly 
named.  This,  however,  is  not  all.  Suppose  that,  in  any  district  of 
England,  three  masses  of  rock  occur,  each  of  which  is  characterized 
by  a  distinctive  group  of  fossils.  Let  these  be  denoted,  for  sim- 
plicity of  reference,  as  A,  B,  C,  and  let  A  represent  the  highest  and 
C  the  lowest  mass — which  means,  naturally,  that 
C  is  the  oldest  and  A  is  the  newest  of  the 
three.  Suppose,  then,  that  the  same 
three  groups  of  fossils  are  discovered 
in  some  other  country — such  as  in  Bel- 
gium or  in  one  of  the  more  distant 
parts  of  France — i;hey  will  always  occur 
in  the  order  A,  B,  C;  never  in  any 
other.  It  is  not,  indeed,  necessary 
that  all  should  occur:  B  may  be  mis- 
sing. But  then  A  will  overlie  C,  and 
a  careful  examination  will  show  that 
it  does  not  follow  immediately — that 
there  is  a  distinct  gap  in  the  record — 
that  a  page,  so  to  say,  has  been  torn 
out  of  the  volume.  The  prin- 
ciple of  regular  sequence  thus 
indicated  is  found,  on  further 
investigation,  to  hold  good  uni- 
versally, so  that  it  can  be  enun-  FlG 
ciated  as  a  general  law  that 

the  order  of  succession   among  extinct    creatures  which  has  been 
established  in  one  region  of  the  earth  is  true  for  all. 

As  this  is  so — as  the  life-history  of  the  past  runs  in  a  regular 
series,  chapter  by  chapter — the  attempt  to  satisfy  inquiries  by  the 
assertion  that  fossils  are  the  relics  of  a  universal  deluge  is  soon 
proved  to  be  futile.  No  such  catastrophe,  even  if  the  language  of 
poetry  be  regarded  as  sober  prose,  could  explain  the  vast  abun- 
dance of  fossils,  and  their  occurrence  in  a  definite  order  in  masses 
of  rock  the  thickness  of  which  can  be  measured  by  thousands  of 
feet.  Gaps  there  may  be  in  the  record,  interruptions  here  or  there 
to  its  continuity,  difficulties  in  harmonizing  every  detail,  or  in 
bringing  the  annals  of  different  countries  into  perfect  parallelism. 
Such  exist  also  in  the  history  of  our  own  race,  and  they  become 


SEQUENCE  OF  MASSES  OF  ROCK. 


8  THE   STORY  OF  OUR  PLANET. 

more  frequent  as  we  approach  the  twilight  of  the  dawn ;  but  in  the 
one  case,  as  in  the  other,  patient  research  and  careful  induction 
have  been  not  without  their  due  reward,  and  many  a  page  in  the 
chronicles  of  the  earth,  no  less  than  in  the  annals  of  nations,  has 
been  already  deciphered. 

This  is  the  history  which  we  must  try  to  tell;  our  task  it  is  to 
give  some  idea  of  the  processes  by  which  the  earth  has  been  molded 
and  shaped  into  the  stage  on  which  all  the  tragedy  and  all  the 
comedy  of  human  life  have  been  enacted.  So,  as  we  have  to  tell 
the  story  of  our  planet,  a  few  words  at  the  outset  must  be  said 
about  the  earth  as  a  planet — that  is,  as  to  its  form,  mass,  and  its 
position  in  the  solar  system.  The  earth  is  a  globe.  The  question 
of  its  form  has  been  so  thoroughly  threshed  out  that,  though  a  few 
advocates  of  a  contrary  opinion  have  existed  within  the  memory  of 
man,  possibly  may  still  linger — for  what  crotchet,  what  mental 
fungus,  cannot  find  a  congenial  soil  in  the  present  age? — it  is  need- 
less to  repeat  the  proof  which  every  text-book  contains.  The 
earth,  however,  is  not  a  perfect  sphere.  Apart  from  the  minor 
inequalities  of  its  surface,  its  form  is  more  nearly  that  of  a  spheroid 
of  revolution — the  figure  generated  by  an  ellipse  revolving  about 
its  shorter  axis.  The  difference,  however,  is  not  great — the  polar 
diameter  of  the  earth  measuring  7,899.37  miles,  the  equatorial 
7,925.82  miles.  Thus  the  greatest  thickness  of  the  equatorial  pro- 
tuberance, as  it  is  called,  of  the  bulging  mass  which  distinguishes 
our  globe  from  a  perfect  sphere,  is  just  under  13*^  miles,  which, 
however,  is  considerably  more  than  twice  the  height  of  the  loftiest 
peak  upon  the  world's  surface. 

The  earth  moves  in  an  orbit  about  the  sun  at  a  pace  which  far 
exceeds  that  of  the  quickest  express — no  less  than  19  miles  a 
second.  It  rotates,  at  the  same  time,  about  its  polar  diameter, 
making  one  complete  turn  in  23  hours  56  minutes  4  seconds.  Dur- 
ing this  period  it  has  changed  its  position  in  the  orbit,  so  that  in 
order  to  bring  any  place  on  the  globe  into  exactly  the  same  posi- 
tion with  regard  to  the  sun,  a  little  more  turning  is  required,  and 
the  day,  thus  measured,  consists  of  24  hours.  After  having  turned 
366  times  on  its  axis,  and  having  been  illuminated  365  times  by  the 
sun,  the  earth  has  come  back  to  the  same  position  in  its  orbit,  and 
a  solar  year  has  been  completed.  But  the  diameter  of  the  earth, 
about  which  it  revolves,  is  not  at  right  angles  to  the  plane  of  the 
orbit — it  is  inclined  at  an  angle  of  23°  28'  (nearly).  This,  as  is  well 
known,  produces  the  summer  and  winter  seasons  and  the  variation 


INTRODUCTORY.  9 

in  the  length  of  day  and  night.  The  orbit  is  an  ellipse,  and  the 
sun  is  placed,  not  at  the  center,  but  in  one  of  the  foci.  Thus  the 
distance  of  the  earth  from  the  sun  is  not  always  the  same;  indeed  it 
changes  not  only  at  different  times  of  the  year,  but  also  from  year 
to  year,  though  very  slowly.  At  present  when  the  earth  is  nearest 
to  the  sun  the  distance  is  91,100,000  miles;  when  it  is  furthest 
away  this  attains  to  94,600,000  miles :  the  average  or  mean  distance 
is  reckoned  as  92,700,000  miles.  The  mind  can  hardly  grasp  the 
notion  of  distances  so  vast;  we  can  appreciate  them  better  if  we 
remember  that  light  itself  takes  eight  minutes  and  sixteen  seconds 
in  traveling  from  the  sun  to  the  earth,  and  that  were  it  possible  for 
sound  to  travel  so  far,  before  the  cry  of  a  newborn  babe  could  reach 
the  sun  the  child  would  be  fifteen  years  old. 

The  earth,  as  we  all  know,  has  an  attendant  satellite — the  moon — 
a  globe  about  2160  miles  in  diameter.  This  revolves  about  the 
earth  as  it  does  about  the  sun,  at  a  distance  of  238,793  miles,  com- 
pleting a  revolution  in  a  period  of  27^  days;  it  rotates  upon  its 
axis  in  the  same  amount  of  time,  so  as  to  present  always  the  same 
face  to  the  earth.  But  the  earth  is  only  one  of  a  number  of  planets 
which  revolve  in  like  way  about  the  sun.  Of  these,  two  are  nearer 
neighbors  than  our  globe;  five  are  further  away.  They  differ  from 
the  earth  in  size  and  in  other  respects.  The  planet  nearest  to  the 
sun  is  called  Mercury,*  which  has  a  diameter  of  2992  miles;  next 
comes  Venus,  which  has  a  diameter  of  7660  miles,  and  so  is  very 
nearly  the  size  of  our  own  planet.  More  distant  than  the  latter 
from  the  sun  is  Mars;  it  has  a  diameter  of  4200  miles,  and  is 
attended  by  two  moons,  which,  however,  complete  their  journey 
round  it  in  a  much  shorter  time  than  our  own  satellite.  Jupiter  is 
next  in  orderf — a  huge  mass,  85,000  miles  in  apparent  diameter — 
attended  by  five  moons,  one  of  which,  however,  is  very  tiny. 
Saturn  comes  next,  accompanied  by  eight  satellites,  and  distin- 
guished by  a  ring,  triple  in  structure  and  a  hundred  miles  in  thick- 
ness. This  planet  is  somewhat  smaller  than  Jupiter,  for  its  diame- 
ter is  71,000  miles.  The  next  planet,  Uranus,  is  attended -by  four 
moons,  but  it  is  considerably  smaller  than  Saturn,  its  diameter 
being  about  32,000  miles.  The  series  is  closed  by  Neptune,  which 

*Some  astronomers  are  of  opinion  that  a  small  planet  has  been  detected  between 
Mercury  and  the  sun.  Its  existence,  however,  cannot  be  regarded  as  proved;  indeed, 
many  attach  little  value  to  the  evidence  which  has  been  adduced. 

\  In  the  interval  comes  a  group  of  planetary  bodies,  comparatively  small  in  size,  called 
the  asteroids.  It  has  been  suggested  by  some  astronomers  that  they  may  be  the  ruins  of  a 
single  large  planet. 


10  THE   STORY  OF  OUR  PLANET. 

is  nearly  the  same  size  as   Uranus,  having  a  diameter  of  34,500 
miles.     It  has  at  least  one  satellite.* 

It  would  be  easy  to  cite  the  distances  of  each  of  these  planets 
from  the  sun,  but,  as  we  have  already  said,  the  mind  can  hardly 
appreciate  millions  of  miles:  a  clearer  notion  can  be  gathered  from 
an  illustration  which  many  years  since  was  given  by  a  famous 
astronomer,  Sir  John  Herschel.  In  the  middle  of  a  wide  and  level 


FIG.  4. — COMPARATIVE  SIZE  OF  THE  SUN  (S)  AND  THE  EARTH  (E). 

plain,  place  a  globe  2  feet  in  diameter.  Take  this  to  represent 
the  sun.  From  it,  as  a  center,  suppose  a  circlef  drawn  with  a 
radius  of  82  feet,  and  a  grain  of  mustard  seed  laid  upon  any  part  of 
the  curve.  These  represent  Mercury  and  its  orbit.  Draw  another 
circle,  with  a  radius  of  142  feet,  and  on  it  put  a  pea.  That  is 
Venus.  Draw  a  third  circle,  with  a  radius  of  215  feet,  and  put 
theron  another  pea.  That  is  the  earth.  On  a  fourth  circle,  with  a 
radius  of  327  feet,  lay  the  head  of  a  large  pin.  That  may  repre- 
sent the  planet  Mars.  Now  a  long  interval  must  be  left,  but  this, 
in  order  to  give  a  complete  representation  of  the  solar  system, 
should  be  interrupted  by  a  number  of  circles,  with  radii  varying 
from  500  to  600  feet,  on  each  of  which  a  grain  of  sand  is  laid ;  these 
would  stand  for  the  asteroids.  Then,  at  a  distance  of  nearly  a 
quarter  of  a  mile  from  the  model  of  the  sun,  draw  a  circle,  and 

*  Authorities  are  by  no  means  in  complete  accord  as  to  the  numbers  given  in  the  above 
paragraph,  so  that  those  quoted  must  be  regarded  as  approximate. 

•  The  planetary  orbits  are  ellipses,  but  as  the 'scale  is  so  small,  the  error  in  representing 
them  by  circles  is  almost  inappreciable. 


INTRODUCTORY.  II 

place  on  it  a  moderate-sized  orange.  This  is  Jupiter.  The  next 
circle  must  have  a  radius  of  two-fifths  of  a  mile,  and  Saturn  may  be 
indicated  by  a  fairly  large  "tangerine."  Lastly,  small  plums  may 
serve  to  represent  Uranus  and  Neptune,  and  for  each  circles  must 
be  drawn,  the  one  with  a  radius  measuring  three-fourths  of  a  mile, 
the  other  with  a  radius  of  as  much  as  i  */£  mile. 

The  weight  of  the  earth  as  a  whole  is  between  five  and  six  times 
as  great*  as  if  it  consisted  throughout  of  water,  supposing  the  fluid 
to  be  incompressible.  Of  the  other  planets  some  are  heavier,  some 
lighter,  bulk  for  bulk,  than  the  earth.  The  four  great  bodies 
appear  to  be  formed  of  material  comparatively  light ;  but  the 
weight  of  this  may  be  somewhat  underestimated,  because  observers, 
in  calculating  the  size  of  the  planet,  may  have  failed  to  distinguish 
between  its  actual  globe  and  the  denser  portions  of  its  atmosphere. 
Into  these  questions,  however,  it  is  needless  to  enter,  since  they 
have  no  direct  connection  with  the  history  of  our  own  planet. 

The  solid  earth,  as  everyone  knows,  is  incompletely  covered  by  a 
shell  of  water,  which  also  traverses  the  dry  land  in  streams,  and 
sometimes  spots  its  surface  with  lakes.  A  gaseous  envelope  sur- 
rounds the  whole — namely,  the  air  which  we  breathe.  Thus  the 
history  of  our  planet,  if  the  problem  be  completely  investigated, 
must  be  studied  in  each  of  these  three  regions;  for  though  ocean 
and  air  may  be  small  in  volume  compared  with  the  solid  globe, 
though  their  effects  upon  it  at  any  great  depth  may  be  insignifi- 
cant, yet  upon  its  surface  they  are  all  potent,  and  it  is  with  this 
that  man  is  mainly  concerned,  for,  after  all,  he  is  but  as  a  parasite 
on  its  cuticle. 

*  The  specific  gravity  of  the  earth  is  about  5.6  ;  that  of  iron  is  7.4 ;  that  of  magnetite 
or  hematite  (common  ores  of  iron),  4.8.  So  the  earth  is  rather  heavier,  bulk  for  bulk, 
than  these  ores. 


CHAPTER  II. 

THE   LAND   REGION. 

THE  land  is  man's  natural  abode,  so  it  shall  be  described  first, 
though  it  occupies  only  about  three-tenths  of  the  surface  of  the 
globe,  for  the  area  of  dry  land  is,  roughly,  55,000,000  square  miles; 
of  the  ocean,  137,200,000.  Taking  the  mean  level  of  the  ocean  as 
a  plane  of  measurement,  we  find  that  its  average  depth  much 
exceeds  the  average  height  of  the  land.  It  has  been  estimated 
that  the  latter  amounts  to  2252  feet,  or  a  little  more  than  375 
fathoms — that  is,  the  height  of  the  uniform  plateau  which  would  be 
formed  if  every  mountain  chain  were  dug  down  and  the  materials 
were  spread  out  over  the  lowlands — if  the  two  processes  of  leveling 
up  and  leveling  down  were  employed  till  .all  inequalities  had  disap- 
peared, and  the  earth's  surface  had  attained  to  the  Socialistic  ideal. 
Though  the  summits  of  mountain  chains  reach  a  much  greater 
elevation,  though  peaks  in  the  Andes  surpass  20,000  feet,  and  the  icy 
crown  of  Mount  Everest,  the  king  of  the  Himalayas,  even  rises  to 
29,000  feet  above  the  sea,  yet  the  greater  part  of  the  dry  land,  as 
it  now  exists,  lies  comparatively  low,  84  per  cent,  of  the  whole  sur- 
face being  less  than  6000  feet — a  thousand  fathoms — above  sea 
level.  To  one  who  has  gazed  at  the  giant  peaks  of  the  Alps,  as 
they  tower  on  high  above  the  lowlands  of  Switzerland  or  the  plains 
of  Northern  Italy,  this  statement  may  seem  almost  incredible,  but 
it  is  affirmed  that  if  the  whole  mass  of  the  Alpine  chain  were 
spread  out  over  Europe  alone  it  would  not  increase  the  elevation 
of  that  continent  by  more  than  22  feet.  The  average  depth  of  the 
depression  occupied  by  the  ocean  is  14,640  feet;  this  is  nearly  equal 
to  the  height  which  the  Matterhorn,  so  familiar  to  most  Alpine 
travelers,  attains  above  its  surface.  Less  than  half  the  ocean 
bed  (42  per  cent.)  lies  within  soundings  of  a  thousand  fathoms, 
and  an  appreciable  portion  (about  2  per  cent.)  exceeds  3000 
fathoms,  the  greatest  known  depth  being  4655  fathoms,  or  about  a 
thousand  feet  less  than  the  height  of  the  loftiest  mountain  peak 


TffE  LAttD  bZGlON.  13 

above  it.  If  the  waters  of  the  ocean  were  gathered  together  into  a 
solid  mass  they  would  form  a  globe  about  850  miles  in  diameter. 

Thus  the  depressions  occupied  by  seas,  as  it  is  important  to 
remember,  are  on  a  far  grander  scale  than  the  mountain  chains. 
The  greatest  height  above  the  sea  level  and  the  greatest  depth 
below  it  are  nearly  equal,  but  if  we  drew  two  contour  lines  on  a 
large  globe — one  a  thousand  fathoms  above,  another  a  thousand 
fathoms  below  sea  level — less  than  i^  per  cent,  of  the  whole  sur- 
face would  lie  above  the  former,  and  nearly  22^  per  cent,  below 
the  latter;  in  other  words,  an  ocean  basin  is  a  physical  feature  on 
the  earth's  crust  of  much  more  significance  than  any  continental 
elevation. 

Both,  however — and  this  is  no  less  important  to  remember — are 
inequalities  almost  trifling  when  compared  with  the  whole  mass  of 
the  globe.  To  the  crawling  caterpillar  the  molehill  seems  a  moun- 
tain ;  to  the  limited  vision  of  man  that  wall  of  snowclad  peaks 
which  bars  his  horizon  from  the  ramparts  of  Berne  or  from  the 
battlements  of  the  Duomo  in  Milan  seems  of  stupendous  vastness. 
Some  scale  more  comprehensible  by  our  senses  must  be  adopted  in 
order  to  dispel  the  glamour  of  crag  and  glacier.  Suppose,  then, 
that  a  globe  has  been  constructed  with  a  diameter  of  a  hundred 
feet,  which  is,  roughly,  equal  to  that  of  the  dome  of  St.  Paul's 
Cathedral,  and  that  on  its  surface  the  mountains  of  the  earth  have 
been  modeled,  and  the  depths  of  the  ocean  have  been  excavated,  in 
each  case  on  a  true  scale.  Then  the  peak  of  Mont  Blanc  would 
rise  less  than  half  an  inch  above  the  original  level,  the  summit  of 
Mount  Everest  itself  would  be  not  quite  nine-tenths  of  an  inch 
above  it,  and  the  ocean  would  be  lodged  in  a  shallow  depression, 
much  of  which  would  vary  from  half  an  inch  to  an  inch  in  depth. 
But,  as  perhaps  even  the  dome  of  St.  Paul's  may  be  rather  too  large 
an  object  for  our  mental  gasp,  let  us  take  a  globe,  such  as  is  com- 
monly sold,  two  feet  in  diameter.  Suppose  that  the  attempt  be 
made  to  model  on  its  surface  the  mountain  chains  and  the  ocean 
depths  of  the  earth.  On  such  a  scale  the  summit  of  the  highest 
peak  will  be  represented  by  a  thickness  of  about  seventeen-thou- 
sandths  of  an  inch — that  is  to  say,  the  difference  between  the 
greatest  height  above  and  the  greatest  depth  below  the  sea  level 
will  be  represented  roughly  by  about  three-hundredths  of  an  inch. 
All  the  inequalities  of  the  land  surface  would  have  to  be  sculptured 
in  the  thickness  of  an  ordinary  playing  card.  So  we  can  realize 
that  the  greatest  of  these — the  loftiest  mountain  peak  or  the  pro- 


THE  LAND  REGION.  15 

foundest  depth  of  ocean — are  insignificant  compared  with  the 
earth's  mass  as  a  whole ;  that  no  change  in  the  position  of  land  and 
of  water,  no  replacement  of  seas  by  mountain  chains,  of  continents 
by  oceans,  is  likely  to  produce  any  material  effect  upon  the  stability 
of  the  earth's  axis  of  rotation. 

Certain  peculiarities  in  the  forms  of  the  existing  continents  and  in 
the  distribution  of  the  seas  can  be  more  conveniently  discussed  in 
later  chapters,  but  one  or  two  others  may  be  mentioned  in  passing. 
The  more  distinctly  elevated  lands — in  other  words,  the  mountain 
regions — are  commonly  restricted  to  comparatively  narrow  belts  on 
the  earth's  surface,  and  rise  with  some  steepness  from  the  lower 
ground.  The  Alps,  for  instance,  occupy  a  zone  from  a  hundred  to 
a  hundred  and  twenty  miles  in  breadth.  As  the  highest  peaks  do 
not  quite  attain  to  an  elevation  of  three  miles  vertical,  the  average 
slope  cannot  exceed  one  in  twenty,  and  is  generally  less.  The 
crest,  however,  of  a  chain  seldom  corresponds  exactly  with  the 
middle  line  of  the  tract  which  it  covers,  so  that  the  average  steep- 
ness of  one  slope  generally  exceeds  that  of  the  other.  Thus  the 
gradient  on  the  western  side  of  the  Andes  is  said  to  be  one  in 
forty,  but  on  the  other  it  is  less  than  one-half  this  amount,  or  one 
in  eighty-three. 

A  linear  group  of  mountains  forms  a  range ;  two  or  more  parallel 
ranges  in  close  connection  constitute  a  chain.  Isolated  mountains 
of  any  importance  are  comparatively  rare,  and  when  they  occur  are 
generally  volcanic — that  is,  are  gigantic  heaps  of  ash  and  slag  piled 
up  around  some  orifice  in  the  crust  of  the  earth.  Sometimes,  how- 
ever, hills,  and  even  mountains,  of  "circumdenudation"  may  be 
found — isolated  fragments  of  far  larger  masses  of  rock,  the  rest  of 
which  has  been  removed,  as  will  be  hereafter  explained,  by  the 
carving  tools  of  Nature".  A  marked  instance  of  such  a  mountain  is 
Roraima,  in  British  Guiana,  an  insulated  mass  which  rises  precipi- 
tously above  the  tropical  forests,  like  some  vast  hill-fortress,  to  a 
height  of  about  7500  feet. 

Almost  every  part  of  an  important  land  mass,  as  might  be  antici- 
pated, is  above  the  level  of  the  sea,  but  a  few  localities  may  be 
found  which  are  exceptions  to  this  rule.  Such  are  considerable 
portions  of  the  Aralo-Caspian  basin,  which  lie  at  various  depths 
below  the  level  of  the  ocean,  amounting  at  most  to  a  little  over 
80  feet.  The  lower  part  of  the  Jordan  valley  is  a  still  more 
remarkable  exception,  for  the  whole  course  of  that  river,  from  the 
neighborhood  of  Lake  Huleh  downward,  is  below  the  Mediter- 


1 6  THE   STORY  OF  OUR  PLANET. 

ranean,  the  surface  of  which  is  almost   1300  feet  above  that  of  the 
Dead  Sea.* 

Before  quitting  for  a  time  the  subject  of  the  dry  land,  one  or  two 
peculiarities  in  its  distribution  over  the  surface  of  the  globe  may  be 
briefly  noticed.  The  continental  masses  are  mainly  restricted  to 
the  northern  hemisphere ;  they  do  not,  however,  appear  to  stand  in 
any  direct  relation  to  its  pole,  except  that  in  the  regions  adjoining 
this  water  apparently  dominates  over  land.  Recent  discoveries  in 


FIG.  6.— A  VOLCANIC  HILL  (VESUVIUS,  FROM  THE  SEA). 

the  North  of  Greenland  seem  to  demonstrate  that  it  is  a  large 
island,  the  shores  of  which  do  not  extend  northward  beyond  about 
82°.  No  great  amount  of  continental  land  projects  north  of  the 
seventieth  parallel  of  latitude;  Greenland,  with  the  large  islands 
to  the  west  of  it,  Spitzbergen  and  Nova  Zembla,  are  almost  the 
only  land  areas  of  importance  known  to  occur  between  that  parallel 
and  the  North  Pole.  The  contrary  conditions  probably  prevail  at 
the  southern  pole;  this  seems  to  be  surrounded  by  a  considerable 
mass  of  land  which  may  comedown  in  places  to  about  the  Antarctic 
Circle.  But  between  its  shore  and  the  fortieth  parallel  of  latitude 

*  The  level  of  the  Dead  Sea  varies  about  five  feet,  according  to  the  season  of  the  year  ; 
the  average  difference  between  it  and  the  surface  of  the  Mediterranean  by  the  last  measure- 
ment was  1292  feet. 


THE  LAND  REGION. 


FIG.  7. — LAND  HEMISPHERE. 


very  little  land  occurs,  while  in  the  northern  hemisphere  considera- 
bly less  than  half  this  zone  is  occupied  by  water.  But  the  most 
marked  contrast  in  the  distribution  of  land  and  water  is  afforded  by 
taking  London  as  a  pole,  and  dividing  the  globe  into  two  hemi- 
spheres. The  one  around  our  metropolis  includes  almost  the 
whole  of  the  great  continental 
masses,  all  Europe,  Africa,  and 
North  America,  almost  all  Asia, 
and  far  the  greater  part  of  South 
America.  The  other  hemisphere 
contains  only  Australia  and  the 
Australasian  Islands,  a  bit  of 
the  Malay  peninsula,  New  Zea- 
land, South  America  about  as  far 
as  Buenos  Ayres,  with  whatever 
land  may  surround  the  southern 
pole.  It  is  also  remarkable  that 
the  land  masses  exhibit  a  general 
tendency  to  become  narrow 
toward  the  south,  and  to  throw 

off  peninsulas  running  in  the  same  direction.  In  the  case  of  three 
great  land  masses — Africa,  South  America,  and  Australia  (if  Tas- 
mania be  included) — it  has  been  further  observed  that  their  pointed 
ends  lie  at  about  equal  distances  one  from  another  on  a  circle,  the 
normal  to  which  makes  an  angle  of  10°  with  the  South  Polar  axis, 
and  that  another  circle,  similarly  situated  in  regard  to  the  North 
Pole,  passes  through  most  of  the  great  inland  seas  and  large  lakes. 
It  is  possible  that  each  of  these  regions  may  indicate  zones  of 
depression  on  the  crust  of  the  earth. 

Attention  also  may  be  called  to  another  fact,  the  significance  of 
which  will  be  discussed  in  a  later  part  of  this  volume — that  a  rela- 
tion evidently  exists  between  mountain  chains  and  the  beds  of  seas 
or  oceans.  This,  on  a  comparatively  small  scale,  is  well  exempli- 
fied in  the  Alps.  The  shallow  basin  of  the  Adriatic,  with  the  plain 
of  the  Po,  is  bordered  by  the  Apennines,  the  Alpine  chain,  and  its 
prolongations,  the  Dinaric  and  Julian  Alps.  A  depression  of  about 
two  hundred  feet  would  bring  out  a  relationship  yet  more  curious. 
Italy  is  often  familiarly  compared  to  a  boot.  By  this  change  of 
level  the  likeness  would  be  undisturbed,  but  the  sea  also  would 
present  the  outline  of  a  second  boot,  and  thus  complete  the  pair. 
The  relationship,  however,  of  mountains  and  oceans  is  not  always 


iS 


THE   STORY  OF  OUR  PLANET. 


FIG.  8.— OCEAN  HEMISPHERE. 


conspicuous  where  the  continents  are  complicated  in  form,  like 
Europe  and  Asia.  In  the  case  of  the  latter  the  enormous  moun- 
tain mass,  which  radiates  from  the  "roof  of  the  world"  (the 
Pamirs):  the  Hindukhush,  with  all  the  highlands  of  Afghanistan; 
the  vast  chains  of  the  Himalayas,  the  Karakorams  and  the  Kuen- 

lun,  with  the  plateaus  of  Thibet, 
which  themselves  overtop  most 
European  peaks;  the  gigantic 
mass  of  the  Thian  Shan,  with  its 
prolongations;  and  the  deserts 
of  Eastern  Turkestan  and  Gobi — 
these,  indeed,  cannot  be  brought 
into  very  close  relation  with  the 
Indian  or  the  Pacific  oceans ;  but 
in  the  case  of  the  three  more 
simply  formed  continents — North 
America,  South  America,  and 
Africa — no  such  difficulty  exists. 
In  all  these  the  important 
mountain  chains  border  the  oceans,  and  the  grander  chains  rise 
near  the  margins  of  the  greater  oceans.  Compare,  in  North 
America,  the  Appalachians,  on  the  Atlantic  border,  with  the  vast 
composite  mountain  mass  which  runs  parallel  with  the  Pacific  from 
one  end  of  the  continent  to  the  other.  The  same  is  true  of  South 
America.  Much  high  ground,  no  doubt,  exists  near  the  Atlantic 
coast,  especially  in  Brazil,  but  this  is  dwarfed  by  the  towering  vol- 
canic summits  of  the  Andes,  many  of  which  overtop  Mont  Blanc,  in 
some  cases  by  more  than  five  thousand  feet.  The  main  watershed 
of  the  country  lies  far  away  to  the  west ;  from  its  crest  the  ground 
on  that  side  may  be  said,  with  little  exaggeration,  to  plunge  down 
to  the  sea,  while  from  its  other  flank  the  great  rivers  flow  to  the 
Atlantic  almost  across  the  continent.  Africa  exhibits  the  same 
characteristic  of  mountains  running  parallel  with  the  coast;  but  as 
the  Indian  Ocean  and  the  Atlantic  are  more  nearly  equal  in  impor- 
tance, the  two  groups  of  chains  differ  less,  and  the  general  struc- 
ture of  the  country,  probably  owing  to  other  causes,  exhibits  more 
complications.  But  the  relation  of  continental  masses  and  ocean 
basins  involves  many  questions  of  extreme  difficulty,  and  even  an 
attempt  to  discuss  it  must  be  postponed  to  a  later  occasion.  At 
present  it  may  suffice  to  observe  that  extensive  basins  of  inland 
drainage — that  is  to  say,  areas  from  which  there  is  no  outflow  to 


THE  LAND  REGION-.  19 

the  ocean — are  by  no  means  rare  on  some  of  the  continents. 
There  is,  among  others,  the  neighborhood  of  Lake  Titicaca,  in 
South  America ;  the  region  between  the  Rocky  Mountains  and  the 
Sierra  Nevada,  including  the  Great  Basin  of  Utah,  in  North 
America;  the  districts  around  Lake  Tchad  and  Lake  Ngami,  in 
Africa;  and  extensive  tracts  in  Australia.  No  such  basins  occur  in 
Europe,  but  they  abound  in  Asia.  Not  only  are  there  the  districts 
of  the  Dead  Sea,  the  Aral,  and  the  Caspian — parts  of  which,  as 
already  said,  are  actually  below  the  sea  level — but  there  are  vast 
regions  above  it,  sometimes  at  great  altitudes;  such  are  lakes  Van 
and  Urmia,  the  Plateau  of  Iran,  and  the  Mongolian  Desert,  with 
Eastern  Turkestan  and  Western  Thibet,  the  last  forming  a  rudely 
rhombic  area,  perhaps  as  large  as  European  Russia. 

The  crust  or  solid  external  part  of  the  earth  is  composed  of 
minerals.  A  mass  of  minerals,  whether  it  consists  of  several  or  of 
one  only  (commonly  the  former),  is  called  a  rock.  With  this  word 
an  idea  of  coherence  and  solidity  is  popularly  associated,  but  in 
geology  that  is  not  so.  The  material  of  a  Lancashire  sand  hill  and 
that  of  the  cliffs  of  Snowdon  are  equally  rock,  in  the  scientific  sense 
of  the  word,  and  in  this  sense  it  will  be  used  in  the  following  pages. 
Hereafter  something  will  be  said  about  the  history  of  rocks  and  the 
modes  in  which  they  have  been  formed ;  at  present  a  few  words 
may  suffice  in  explanation  of  certain  terms  which  it  will  be  needful 
to  employ  occasionally  in  the  earlier  part  of  this  book. 

Rocks  may  be  divided  into  two  principal  groups:  those  which 
have  solidified  from  a  fused  condition,  and  those  formed  of  con- 
stituents more  or  less  gradually  deposited.  The  former  are  called 
igneous  rocks;  they  vary  in  mineral  composition  and  in  texture. 
Most  of  them  are  more  or  less  distinctly  crystalline — that  is  to  say, 
are  composed  of  individual  minerals,  which  have  gradually  segre- 
gated out  of  the  molten  mass — but  in  some  a  crystalline  structure 
is  practically  not  to  be  distinguished.  Granite  is  an  example  of 
the  former  kind,  felstone  of  the  latter;  some,  however,  like 
obsidian,  are  true  glasses.  Yet  these  three  rocks  may  contain  the 
same  constituents  in  the  same  proportions — may  be  chemically 
identical.  The  differences  between  them  are  due  to  their  environ- 
ment, to  the  circumstances  under  which  they  have  cooled.  When 
the  loss  of  heat  has  been  rapid  the  rock  is  glassy,  and  often  porous 
or  slaggy.  With  a  more  gradual  fall  in  temperature,  the  mass 
assumes  a  more  solid  and  more  crystalline  condition. 

As  the  rocks  in  the  second  group  are  almost  always  deposited,  , 


20  THE   STORY  OF  OUR   PLANET. 

more  or  less  directly,  by  the  action  of  water,  they  are  concisely 
designated  "aqueous  rocks,"  though  a  few — such  as  blown  sands 
and  the  piles  of  dust  and  lapilli  ejected  from  volcanoes — have  been 
transported  by  wind  instead  of  water.  Still  as  it  may  be  argued 
that  air  at  any  rate  is  a  fluid,  and  that  in  many  cases  steam  rather 
than  wind  has  caused  an  accumulation  of  volcanic  ashes — for  the 
fragments  may  lie  as  they  fell  about  the  crater  after  an  explosion — 
no  misapprehension  of  importance  is  likely  to  be  caused  by  the 
extended  use  of  the  term.  Aqueous  rocks  may  be  subdivided  into 
(i)  those  which  have  been  precipitated  from  solution  in  water — 
such  as  rock  salt,  gypsum,  and  travertine ;  (2)  those  which  have 


FIG.  9.— BLOCK  OF  PUDDING  STONE. 

been  deposited  by  water  as  fragments  broken  originally  from  other 
rocks — such  as  gravel,  pudding  stone,  sandstone,  clay,  and  shale ; 
and  (3)  those  which  are  composed  wholly,  or  almost  wholly,  of  the 
remains  of  organisms  (generally  accumulated  in  or  under  water) — 
such  as  peat,  coal,  tripoli,  chalk,  and  the  purer  limestones.  It 
must  be  remembered  that  these  sedimentary  rocks,  as  they  are  not 
seldom  called,  cannot  always  be  separated  by  hard  and  fast  lines, 
because  they  may  have  been  formed  by  more  than  one  of  the  above 
processes.  Mud  or  sand  may  be  carried  into  a  sea,  and  may  settle 
down  to  mingle  with  the  relics  of  the  creatures  which  have  lived  on 
its  floor  or  have  tenanted  its  waters.  Precipitation  of  mineral  sub- 
stances may  go  on  together  with  the  accumulation  of  sediment  or 
of  dead  organisms;  so  that,  as  a  rule,  terms  like  sandstone,  mud- 
stone,  and  limestone,  indicative  of  sedimentary  rocks,  cannot  be 
used  with  extreme  precision. 

Most  rocks  which  have  been  deposited  for  a  very  long  time  have 
undergone  some  mineral  change — the  hard  limestone  was  once  a 


THE  LAND   REGION.  21 

soft  ooze,  the  best  honestone  once  a  mud — but  there  are  some 
masses  which  have  been  so  greatly  altered  that  it  is  often  no  easy 
task— and  is  sometimes  almost  impossible — to  determine  what  has 
been  their  original  condition.  Rocks  in  which  such  marked  altera- 
tions have  taken  place  are  called  metamorphic,  and  these  are  gener- 


FIG.   10. — STRATIFIED  ROCKS. 

The  dark  line  running  down  the  face  of  the  cliff  in  front  is  called  a  fault  :  the  mass  to  the  right  of  it 
has  dropped  down.  This  has  preserved  the  bed  /z,  which  has  been  removed  by  denudation  from  the  oppo- 
site side  of  the  fault. 

ally  treated   as   a   separate   or  third   group.     Of  such,  mica-schist, 
quartzite,  serpentine,  and  statuary  marble  are  examples. 

In  sedimentary  rocks,  as  might  be  expected,  their  origin  is  indi- 
cated by  their  structure.  The  materials,  when  fine,  form  thin 
layers,  and  the  rocks  are  then  said  to  be  laminated.  So  long  as 
these  continue  without  variation  in  size  the  rock  mass  increases 
without  any  change.  Its  character  is  altered  when  the  fragments 
become  larger  or  smaller;  a  layer  thus  distinguished  from  that 
immediately  above  and  below  is  called  a  stratum,  and  rocks  formed 
of  such  layers  are  said  to  be  stratified.  Lamination,  indeed,  is  a 
record  of  some  very  slight  check  or  change  in  the  deposit  of 
materials;  stratification  indicates  more  marked  instances  of  the 


22  THE   STORY  OF  OUR  PLANET. 

same.  A  stratum  is  related  to  its  laminae  somewhat  as  a  book  to 
its  leaves.  Sometimes  stratification  can  only  be  detected  on  a 
close  examination ;  sometimes  the  layers  are  as  distinct  as  are  a 
number  of  mattresses  when  laid  in  order  one  on  another.  Fine- 
grained rocks  of  an  almost  homogeneous  or  a  laminated  character, 


• •-  ~°°    -     -"•  "->^          *      -°-:''  "''  <" 


FIG.  ii.— A  CASE  OF  FALSE  BEDDING. 


like  muds  and  shales,  indicate  quiet  deposit ;  irregularities  of  struc- 
ture are  records  of  stronger  and  more  variable  currents.  The  sand 
on  the  shore  or  beneath  the  shallower  water  is  thrown  into  gentle 
undulations  by  the  movement  of  the  waves  or  by  the  action  of  cur- 
rents, whether  in  the  air  or  the  water.  Similar  structures  can  be 
seen  in  such  rocks  as  the  finer  sandstones,  and  are  called  ripple- 
mark.  Strong  and  variable  currents,  like  those  of  a  tolerably  swift 
river,  deposit  coarser  materials,  which  form  shoal-like  banks  com- 
posed of  sloping  zones  of  more  pebbly  and  of  more  sandy  stuff. 
As  portions  of  these  are  often  destroyed  by  changes  in  the  direc- 
tion and  the  velocity  of  the  currents — the  tops  of  the  banks  espe- 
cially being  planed  away — and  as  new  shoals  are  formed  in  rather 
different  positions,  a  mass  of  material  thus  accumulated,  when  it  is 
cut  through  in  a  vertical  direction,  exhibits  a  double  structure,  the 
one,  that  on  the  smaller  scale,  being  indicative  of  the  building  up  of 
the  several  shoals,  the  other,  that  on  the  larger,  being  a  record  of 
the  actual  shoals  (Fig.  u).  As  the  former  often  appeals  more 
quickly  to  the  eye,  especially  when  only  a  limited  section  is 
exposed,  and  would  produce  a  misapprehension  as  to  the  angle  at 


THE  LAND  REGION.  23 

which  the  stratum  was  inclined  to  the  horizon,  the  structure  is 
called  false  bedding.  Some  geologists  use  current  bedding  as  an 
equivalent  term ;  by  others  the  latter  is  applied  to  instances  where 
the  structure  is  more  regular. 

Certain  structures,  called  "joints,"  are  almost  always  exhibited 
by  the  igneous  or  unstratified  rocks  as  well  as  by  the  stratified. 


FIG.   12. — JOINTS  EXHIBITED    IN  A    MOUNTAIN    RUIN,   FROM    THE    DOLOMITES    OF 
CORTINA,  S.E.  TYROL. 

These  are  divisional  planes  separating  the  mass  into  blocks.  The 
latter  may  be  large  or  small,  regular  or  irregular  in  form,  largeness 
and  regularity  commonly  going  together.  In  such  a  case  stratified 
rocks  are  generally  traversed  by  two  sets  of  joints  at  right  angles 
one  to  another  and  to  the  planes  of  bedding  (Fig.  12);  igneous 
rocks  by  three,  so  as  to  form  rectangular  prisms.  In  these  rocks 
four  sets  of  joints  may  be  sometimes  found,  forming  hexagonal 
prisms  (Fig.  13).*  This  is  the  normal  shape,  but  occasionally  the 

*  This  is  often  called  "  columnar  jointing,"  sometimes  "  basaltic  jointing."  The  latter  is 
a  misnomer,  for  the  structure  is  not  restricted  to  basalt,  but  is  found  in  other  fine-grained 
igneous  rocks.  It  has  been  observed  also  in  sedimentary  rocks,  but  here  it  is  generally  the 
result  of  heat,  and  the  prisms  commonly  are  small,  less  than  three  inches  in  diameter.  A 
remarkable  instance  in  a  volcanic  mud,  over  which  a  lava  stream  has  passed,  may  be  seen 
in  Tideswell  Dale,  Derbyshire.  It  can  be  produced  artificially,  but  is  then  generally  quite 


24  THE  STORY  OF  OUR  PLANET. 

number  of  sides  is  greater  or  less  than  six.  The  grand  colonnades 
of  dark  basalt  at  the  Giant's  Causeway,  in  Antrim,  and  about 
Fingal's  Cave,  in  Staffa,  are  striking  examples  of  this  mode  of  joint- 
ing (Fig.  14).  In  the  Siebengebirge  the  basalt  columns  are  so  long 
and  slender  as  to  be  used  for  fingerposts  and  like  purposes.  Joint 
structures  were  helpful  to  man  in  his  first  efforts  at  monumental 
architecture.  By  their  regularity,  but  comparative  infrequency  in 
some  varieties  of  granite,  the  huge  roof  of  the  dolmen  of  Concar- 
neau,  and  the  great  menhir  of  Lokmariaker,  were  rendered  possible, 


FIG.  13.— COLUMNAR  JOINTING. 

no  less  than  the  pillars  of  the  Pantheon  at  Rome,  and  the  yet  vaster 
masses  of  the  Egyptian  obelisks. 

Other  structures  there  are  which  in  due  course  may  receive  fur- 
ther notice.  For  the  present  it  may  suffice  to  say  that  many  rocks 
are  affected  by  a  tendency  to  split  in  a  direction  which  has  no 
necessary  connection  with  their  original  bedding.  This  is  most 
perfect  and  conspicuous  in  rocks  composed  of  very  fine  materials. 
Such  are  called  slates,  and  the  structure  is  named  slaty  cleavage. 
But  it  may  be  seen  also  in  rocks  of  coarser  grain,  though  in  them  it 
is  much  less  uniform  and  regular.  Indeed,  it  has  been  sometimes 
impressed  upon  igneous  rocks,  as  may  be  often  seen  in  mountain 
regions.  Formerly  the  cause  of  this  structure  was  much  disputed ; 
that  it  is  a  result  of  pressure  is  now  generally  admitted. 

Thus  the  crust  of  the  earth,  as  the  most  casual  examination  indi- 
cates, is  composed  of  masses  variable  in  form  and  of  materials 
heterogeneous  in  character.  It  is  like  some  colossal  structure,  in 
the  architecture  of  which  diverse  substances  have  been  employed 
and  different  modes  of  building  adopted.  So  when  this  crust  is 
attacked  by  the  various  forces  of  Nature — the  heat  and  the  cold, 
the  wind  and  the  rain,  the  stream  and  the  wave — it  offers  an 


TffE  LAND  REGION.  25 

unequal  resistance.  As  it  falls  into  ruins  the  varied  constructions 
are  revealed,  as  in  buildings  made  by  the  hand  of  man,  and  every 
shape  of  crag  or  sweep  of  slope,  every  outline  of  peak  or  curve  of 
valley,  is  due  to  the  character  of  the  materials  and  to  the  structures 
of  each  particular  portion  of  the  earth's  crust. 


FIG.  14.— COLUMNAR  BASALT,  FINGAL'S  CAVE. 


CHAPTER  III. 

THE   AIR   REGION. 

THROUGH  the  air  man  moves;  by  it  he  is  ever  surrounded;  on  it 
his  life  depends,  even  more  immediately  than  on  water;  so  this 
region,  often  termed  the  atmosphere,  seems  to  claim  priority  of 
notice  to  that  of  water.  It  differs  from  the  ocean  in  covering  the 
whole  globe,  extending  to  a  height  of  at  least  two  hundred  miles 
above  the  surface  of  the  latter;  but  as  it  rapidly  decreases  in  den- 
sity, and  at  last  becomes  exceedingly  thin,  its  outer  limit  cannot  be 
ascertained.  As  air  has  weight,  the  atmosphere  exercises  a  pres- 
sure upon  the  surface  of  the  earth  and  everything  thereon,  amount- 
ing to  about  fourteen  pounds  on  the  square  inch.  So  the  weight 
of  the  atmosphere  is  equal,  roughly,  to  that  of  a  shell  inclosing  the 
globe,  which,  if  made  of  water,  would  be  30  feet  thick,  or  if  of  an 
average  kind  of  rock  rather  more  than  13  feet  thick. 

Air  consists  of  nitrogen  and  oxygen  gases  in  the  proportion  of 
79  to  21.*  Either  of  these  by  itself  would  quickly  put  an  end  to 
life;  thus  mixed  they  are  essential  to  its  continuance.  Small  and 
variable  quantities  of  water  vapor  and  of  carbonic  acid  gas  are  also 
present — the  former  of  these,  on  an  average,  amounts  to  about  0.45 
per  cent. ;  the  latter  to  much  less,  only  from  three-  to  five- 
hundredths.  Occasionally  other  gases — such  as  sulphuric  acid — are 
locally  present;  these,  however,  may  be  regarded  as  accidental, 
resulting  from  such  causes  as  the  presence  of  large  towns  and  other 
irritations  of  the  earth's  cuticle  for  which  man  is  responsible. 

The  aqueous  vapor  not  only  is  the  immediate  source  of  rain,  but 
also  performs  another  function  of  the  utmost  importance.  Though 
the  interior  of  the  earth  is  at  a  high  temperature,  the  internal  heat 
escapes  so  slowly  that  it  does  not  appreciably  affect  the  surface. 
This  is  warmed  by  the  sun.  The  rays  of  light  and  heat  from  that 
gigantic  furnace  traverse  space  without  appreciably  raising  its 

*  The  proportions  of  dry  air,  neglecting  the  slight  and  mostly  immeasurable  traces  of  the 
other  constituents,  may  be  put  as  follows  :  Oxygen,  20.95  ;  nitrogen,  79.02  :  and  carbonic 
acid,  0.03  parts  to  100  by  volume. — Ferrel,  "  A  Popular  Treatise  on  the  Winds,"  p.  I. 


THE  AIR  REGION.  27 

temperature,  which  is  probably  as  low  as  —  239°  F.  If  the  day 
come,  as  in  the  poet's  vision,  when  "the  sun  itself  shall  die,"  the 
earth,  supposing  the  extinction  to  be  sudden,  would  quickly  cool 
down,  as  a  stone  does  if  removed  from  the  full  glare  of  the  midday 
orb  into  an  icehouse;  life  would  be  impossible,  our  blood,  lungs, 
heart,  would  be  stone,  for  everything  would  be  frozen  solid.  If 
there  were  no  aqueous  vapor  in  the  atmosphere,  considerable  risk 
would  attend  even  the  temporary  withdrawal  of  the  sun's  heat  dur- 
ing the  night  time ;  for  as  it  is,  this,  as  everyone  knows,  causes  a 
marked  fall  in  the  temperature.  The  air  alone  would  avail  but 
little  to  remedy  the  loss;  it  too,  like  the  earth,  would  quickly 
radiate  into  outer  space  the  store  of  heat  accumulated  during  the 
day ;  but  a  safeguard  is  found  in  the  small  quantity  of  aqueous 
vapor  so  generally  present  in  the  atmosphere ;  for  this,  while  fairly 
transparent  to  luminous  heat,  is  opaque  to  radiant  heat — that  is  to 
say,  it  allows  vibrations  emitted  by  the  sun  to  pass  without  appre- 
ciable obstruction,  but  when  the  surface  of  the  darkened  earth 
begins  to  disperse  its  accumulated  store,  the  passage  of  these 
slower  vibrations  is  resisted.  In  other  words,  the  aqueous  vapor 
present  in  the  atmosphere  plays,  as  it  has  been  well  said,  the  part 
of  a  ratchet  wheel  in  machinery.  It  is  always  found  that  the  drier 
the  climate  the  greater  the  difference  between  the  highest  reading 
of  the  thermometer  by  day  and  its  lowest  reading  by  night ;  and  if 
all  the  aqueous  vapor  could  be  suddenly  eliminated  from  the 
atmosphere,  only  for  the  interval  of  a  summer  night,  the  sun  would 
rise  next  morning  on  a  land  petrified  by  frost.* 

The  aqueous  vapor  rapidly  diminishes  in  quantity  after  a  distance 
of  a  very  few  miles  from  the  surface  of  the  earth — the  blanket,  so 
to  say,  is  wisely  worn  nearest  to  the  skin.  The  density  of  the 
atmosphere  also  diminishes.  At  the  sea  level  the  mercurial  barom- 
eter stands  approximately  at  thirty  inches.f  At  elevations  above  it 
the  length  of  the  column  diminishes  as  the  height  of  the  station 
increases,  the  alteration  amounting  very  roughly  to  rather  less  than 
an  inch  for  every  thousand  feet  of  ascent.  At  the  Great  St.  Ber- 

*  The  atmosphere  intercepts  about  four-tenths  of  the  solar  heat  during  the  whole  day, 
but  only  about  one-quarter  when  the  sun  is  in  the  zenith.  The  total  amount  of  heat 
received  by  the  earth  from  the  sun  in  a  year,  if  distributed  uniformly  over  its  surface,  would 
suffice  to  melt  a  layer  of  ice  100  feet  thick  covering  the  whole  earth. — Tyndall,  "  Heat  as 
a  Mode  of  Motion,"  ch.  xiv. 

f  The  average  barometric  pressure  for  all  seasons  and  for  all  parts  of  the  earth's  surface 
is  found  from  observation  to  be  about  760  millimeters  (29.92  inches). — Ferrel,  p.  n. 


28  THE  STORY  of  OUR  PLANET. 

nard  Hospice,  8130  feet  above  the  sea,  the  barometer  stands  at 
22.2  inches;  on  Pike's  Peak,  14,134  feet,  at  17.7  inches;  at  the  sum- 
mit of  .Mont  Blanc,  15,781  feet,  nearly  half  the  atmosphere  by 
weight  lies  below  the  observer;  and  on  the  highest  dome  of  Chim- 
borazo,  which  is  about  20,500  feet  above  the  sea,  Mr.  Whymper  on 
one  occasion  obtained  a  reading  of  14.11,  on  another  of  14.04 
inches  ;*  but  in  Messrs.  Coxwell  and  Glaisher's  highest  ascent,  at 
an  elevation  of  37,000  feet,  the  barometric  reading  was  only  7 
inches. 

The  question  has  been  raised  whether  the  rarity  of  the  air  on  the 
summit  of  such  a  peak  as  Mount  Everest  might  not  prove  fatal, 
and  man  meet  with  the  death  of  a  fish  out  of  water.f  Mr.  Whym- 
per's  observations  in  the  Andes  of  Ecuador  showed  that  though 
exertion  undoubtedly  became  more  difficult,  and  a  painful  initia- 
tion had  to  be  undergone  in  a  region  more  than  16,000  feet  above 
the  sea,  the  vital  powers  were  not  seriously  diminished  even  on  the 
summit  of  Chimborazo. 

But  the  height  of  the  barometer — in  other  words,  the  pressure  of 
the  atmosphere — is  not  uniform  at  all  places  on  the  earth's  surface; 
neither  is  it  steady  from  day  to  day — even  from  hour  to  hour. 
The  causes  of  these  variations  are  complex — dependent  on  condi- 
tions general  as  well  as  local.  As  regards  the  former,  the  atmos- 
pheric pressure  on  the  sea  and  in  its  immediate  neighborhood  is 
rather  less  over  a  zone  about  the  equator  than  it  is  further  to  the 
north  or  south,  a  maximum  being  reached  between  latitudes  30°  to 
35°;  the  average  reading  is,  in  the  one  case,  29.84  inches,  in  the 
other,  30.08  inches.  Then  it  diminishes  slowly  toward  the  poles, 
declining  to  about  29.92  inches  in  latitude  50°,  so  that  beyond  this 
there  is  a  second  low  pressure  area.  The  atmospheric  pressure  at 
the  equator  ought  to  be  greater  than  at  the  poles,  because  a  slight 
heaping  up  of  the  fluid  above  the  former  region  must  be  caused  by 
the  rotation  of  the  earth,  but  the  abnormality  indicated  by  the 
figures  quoted  above  is  possibly  due  to  a  variability  in  the  amount 
of  aqueous  vapor  in  the  atmosphere,  by  which  its  weight  is 

*  Mr.  Conway  informs  me  (while  this  sheet  is  in  the  press)  that  the  lowest  reading  which 
he  obtained  during  his  most  interesting  exploring  expedition  in  the  Karakoram  chain  was 
13.30  inches.  This,  on  comparison  with  a  simultaneous  reading  at  Leh,  gives  an  altitude 
of  22,400  feet. 

f  Messrs.  Coxwell  and  Glaisher  nearly  perished  in  a  balloon  at  a  height  of  about  37,000 
feet.  But  as  the  change  of  level  was  rapid,  this  test  proves  only  the  height  up  to  which 
life  certainly  can  be  continued. 


THE  AIR  REGION-.  2$ 

affected.*  The  diurnal  differences  are  the  result  of  diverse  causes, 
chief  among  which,  in  all  probability,  are  the  increase  or  decrease 
in  the  aqueous  vapor  and  the  rise  or  fall  of  temperature.  In  very 
dry  countries,  such  as  parts  of  Eastern  Siberia,  the  barometer  is 
said  to  rise  by  day  as  the  temperature  increases,  and  fall  by  night 
as  it  declines.  The  isobars  also — or  lines  passing  through  the 
places  on  the  earth's  surface  at  which  the  barometer  stands  at  the 
same  height— exhibit  a  general  correspondence  with  the  diurnal 
isotherms,  or  lines  indicating  the  same  average  daily  temperature. 

The  winds  are  mainly  produced  by  inequality  of  barometric  pres- 
sure. Some  are  approximately  constant  in  direction  and  perma- 
nent in  duration;  others  are  in  action  only  during  certain  seasons; 
while  a  third  set  are  more  variable  and  brief,  but  sometimes  more 
violent. 

Of  the  first  set  the  trade  winds  are  the  principal  examples:  vast 
currents  of  air  of  the  utmost  importance  in  the  economy  of  the 
globe;  the  direct  results  of  the  sun's  heat  in  the  zone  where  its 
rays  are  most  intense.  Here,  over  a  belt  of  variable  breadth,  which 
sometimes  is  little  more  than  150  miles  wide,  but  sometimes  is  fully 
600,  the  air,  when  the  meridian  sun  is  at  or  near  the  zenith,  becom- 
ing heated,  expands  and  rises.  This — a  region  of  light  variable 
airs,  inconstant  in  direction — is  called  the  "zone  of  central  calms."f 
But  as  the  air  rises,  the  equilibrium  of  the  lower  layers  is  dis- 
turbed ;  its  place  is  taken  by  an  inflow  from  either  side  of  the  belt. 
Thus  a  current  is  set  up  which  affects  a  mass  of  air  north  and  south 
of  the  equator.  But  this  is  so  large  that  a  marked  effect  on  the 
direction  of  the  wind  is  produced  by  the  rotation  of  the  earth.  For 
instance,  when  air  starts  on  a  southward  journey  from  latitude  25° 
N.,  it  is  moving  eastward  with  the  same  velocity  as  this  part  of 
the  earth's  surface,  but  it  passes  on  its  course  over  places  which  are 
traveling  at  a  much  greater  rate,  and  is  thus,  as  it  were,  overtaken 
by  them,  and  so,  seemingly,  comes  from  the  east  of  north.  When 
a  steamer  is  crossing  from  Dublin  to  Holyhead,  and  the  wind  is 
blowing  from  the  north,  the  smoke  drifts  toward  the  southwest,  and 
this,  to  anyone  unconscious  of  the  vessel's  motion,  would  indicate 
the  direction  of  the  wind.  So  in  the  region  of  the  northern  trades 
the  breeze  seems  to  come  from  the  northeast.  Similarly  in  that  of 
the  southern  trades  it  apparently  blows  from  the  southeast. 

*  Professor  Ferrel  explains  it  as  being  due  to  a  difference  between  the  rate  of  rotation  of 
the  atmosphere  and  of  the  earth,  which  vanishes  about  latitude  30°  N.  and  S. 
f  Also  "  the  equatorial  calm  belt." 


30  THE   STORY  OF  OUR  PLANET. 

These  currents  of  air  flow,  as  a  rule,  with  a  steady  and  uniform 
motion,  though  disturbawces  are  apt  to  be  produced  by  the  conti- 
nental land  masses;  the  regions,  however,  which  are  affected  by 
them  vary  in  breadth.  This  may  amount  to  as  much  as  thirty 
degrees  of  latitude  in  the  South  Pacific,  but  does  not  exceed  twenty, 
and  is  sometimes  not  quite  so  much,  in  the  North  Atlantic. 

The  course  of  the  air  which  has  mounted  up  from  the  zone  of 
central  calms  has  yet  to  be  traced.  It  wells  up  like  the  water  of  a 
continuous  spring  which  girdles  the  globe.  After  a  time  the  air,  as 
is  the  case  with  water,  ceases  to  rise,  and  flows  northward  and 
southward  over  the  mass  below.  This,  however,  is  traveling  in  the 
contrary  direction  to  replace  that  which  has  risen,  and  its  room 
must  be  occupied;  so,  as  the  upper  current  of  air  is  cooled  by 
radiation  of  its  heat  into  outer  space,  it  becomes  heavier  than  the 
underlying  mass,  and  slowly  settles  down  to  the  earth.  Obviously 
these  currents  on  their  journey  northward  and  southward  will  be 
converted  respectively  into  southwest  and  northwest  winds.  Thus 
a  circulation  of  aerial  currents  in  opposite  directions — a  kind  of 
"endless  cord"  arrangement — is  permanently  established  north  and 
south  of  the  equator,  though  the  area  affected  does  not  remain 
exactly  the  same  during  the  whole  year.  The  belt  of  central  calms 
must  of  course  change  its  position  in  accordance  with  the  apparent 
path  of  the  sun,  so  that  both  it  as  well  as 'the  zones  affected  by  the 
northern  and  southern  trade  winds  must  move  backward  and  for- 
ward.* For  instance,  it  is  supposed  that  the  northern  anti-  or 
counter-trades  descend  in  winter  about  the  latitude  of  Lisbon,  at 
the  equinoxes  about  that  of  Berlin,  and  in  the  summer  they  may 
come  down  even  as  far  north  as  St.  Petersburg.  By  their  descent, 
as  by  their  ascent,  another  zone  of  so-called  calms  is  formed, 
though  here  the  epithet  is  less  strictly  applicable,  for  it  is  rather 
one  of  shifting  winds,  variable  in  force,  but  commonly  light.  The 
division  between  these  moving  masses  of  air — which  itself  will  be  a 
zone  of  variable  and  uncertain  airs,  though  apparently  of  no  great 
vertical  height — must  obviously  approach  the  earth's  surface  as 
the  latitude  increases.  The  lower  current  at  first  affects  the  air  for 
a  height  of  from  four  to  five  miles  vertical,  but  before  reaching  lati- 
tude 30°  N.  its  height  has  greatly  diminished.  An  interesting  illus- 

*  Professor  Ferrel  ("  Popular  Treatise  on  the  Winds,"  p.  159)  gives,  for  the  N.E.  trade 
wind,  a  table  indicating  the  latitude  at  which  it  begins  in  the  four  seasons.  The  extreme 
difference  between  the  summer  and  winter  position  is  about  6°.  According  to  another 
table,  this,  for  the  S.E.  trade,  amounts  sometimes  to  14°. 


THE  AIR  REGION.  31 

tration  is  afforded  by  the  Peak  of  Teneriffe,  which  rises  to  a  height 
of  12,060  feet  above  the  Atlantic.  At  one  season  of  the  year  the 
clouds,  both  on  the  summit  and  the  zone  about  3000  feet  below  it, 
move  from  the  southwest,  indicating  that  this  rises  into  the  region 
of  the  counter-trades,  but  those  on  the  lower  part  of  the  mountain 
are  driven  by  the  trade  wind  from  the  opposite  point  of  the  com- 
pass. A  curious  proof  of  the  existence  of  the  counter-trade 
current  has  been  afforded  by  the. fine,  almost  impalpable,  dust 
which  is  often  shot  up  high  into  the  air  by  the  explosive  force  of  a 
volcanic  eruption.  Such  a  dust  shower  fell  at  Barbadoes  on  a  May 
morning  in  1812  while  the  northeast  trade  wind  was  blowing. 
Neither  in  that  island  nor  in  its  immediate  neighborhood  are  any 
volcanoes.  But  a  day  or  two  before  Morne  Garou,  in  St.  Vincent, 
125  miles  away  to  the  west,  had  broken  out  into  violent  eruption. 
Its  dust  must  have  been  hurled  up  into  the  region  of  the  counter- 
trades, carried  by  them  away  to  the  northeast  beyond  Barbadoes, 
till  it  settled  down  into  the  contrary  air  current,  and  was  then 
blown  back  on  to  that  island.  A  similar  instance  once  occurred  at 
Jamaica,  whither  the  dust  from  Coseguina,  in  Central  America,  800 
miles  away  to  the  southwest,  came  seemingly  in  the  teeth  of  this 
lower  current  of  air.  Round  each  pole  there  is  a  zone  of  low  pres- 
sure, so  that  there  is  some  tendency  to  draw  the  air  which  has 
descended  northward  or  southward  as  the  case  may  be.  But  north 
of  the  belt  of  comparative  calms — named  sometimes  after  the 
circles  of  Cancer  and  Capricorn — at  the  "back"  of  the  trade  winds, 
the  direction  of  the  air  currents  is  shifting  and  uncertain.  The 
annexed  diagram  (Fig.  15)  will  give  a  general  idea  (and  nothing 
more  is  attempted)  of  the  air  circulation  of  the  globe,  the  arrows 
indicating  the  directions  of  movement,  and  those  between  the  circle 
and  the  ellipse  (which  represents,  in  an  exaggerated  form,  the 
atmospheric  boundary)  representing  the  paths  of  the  rising  and 
falling  air. 

Land  masses,  as  has  been  said,  produce  irregularities  in  the  trade 
winds.  Over  mountainous  districts  the  aerial  current  may  be 
forced  up  like  a  stream  of  water  as  it  flows  over  a  bowlder  which 
projects  from  its  bed ;  should  the  summits  attain  a  sufficient  height 
it  might  even  be  diverted.  But  the  land  masses,  by  producing 
variations  of  temperature,  give  rise  to  yet  more  important  changes 
in  direction.  The  temperature  of  the  ocean  as  a  general  rule  is 
fairly  uniform  over  considerable  districts;  its  variations  also  are 
slow,  for  water  both  acquires  and  parts  with  heat  much  less  quickly 


3- 


THE    STORY  OF  OUR  PLANET. 


than  the  materials  of  which  the  earth's  crust  is  usually  composed. 
So  the  air  which  rests  upon  the  surface  of  the  ocean  continues 
much  more  nearly  at  the  same  temperature  by  day  and  by  night, 
and  on  successive  days,  than  that  which  is  above  the  land.  This 
difference  produces  the  great  periodic  winds,  which  in  some  parts  of 


FIG.  15.— DIAGRAM  OF  Am  CURRENTS  AND  ATMOSPHERIC  CIRCULATION. 


the  globe  are  called  monsoons.*  Those  of  Hindustan,  with  which 
English-speaking  folk  are  most  familiar,  are  due  to  the  heating  of 
the  air  above  the  plains  of  India  and  the  plateaus  of  Central  Asia. 
As  the  sun  approaches  the  northern  tropic  the  temperature  of  these 
regions,  which  are  frequently  arid,  is  greatly  raised,  and  the  air 
above  them  becomes  much  heated,  and  rises.  Thus,  precisely  as 
already  described,  a  draught  is  created  which  first  neutralizes,  then 
overpowers,  the  current  of  the  trade  wind.  So  long  as  the  disturb- 
ing influence  remains,  so  long  does  the  monsoon  blow.  As  a 
general  rule,  its  direction  is  opposite  to  that  of  the  trade  wind,  but 
the  precise  quarter  from  which  it  sets  depends  upon  local  circum- 
stances— such  as  the  trend  of  the  coast,  the  configuration  of  the 
land  surface,  and  the  like.  As  the  sun  retreats  southward  the  mon- 

*From  an  Arabic  word  meaning  "  change." 


THE  AIR  REGION.  33 

soon  ceases,  and  in  the  winter  season  the  trade  wind  blows  as  usual. 
But  the  former  is  generally  a  much  shallower  current  than  the  latter ; 
probably  its  influence  never  extends  for  more  than  4000  or  5000  feet 
above  the  earth.  This  is  indicated  by  several  facts  ;  for  instance, 
in  Java  the  "smoke"  from  the  crater  of  a  volcano,  which  rises  to  a 
height  of  about  9000  feet  above  the  sea,  always  drifts  steadily  toward 
the  west  under  the  influence  of  the  trade  wind.  But  for  six  months 
of  the  year  the  clouds  on  the  lower  slopes  of  the  mountain  are  driven 
by  the  monsoon  in  an  opposite  direction.  Winds  similar  to  the 
monsoons  occur  on  the  west  coast  of  Africa,  especially  in  the  Gulf 
of  Guinea,*  in  the  Gulf  of  Mexico,  and  over  considerable  parts  of 
both  coasts  of  South  America.  The  Etesian  winds  of  the  Mediter- 
ranean— northern  breezes  set  up  in  summer  time  by  the  heated 
lowlands  of  Egypt  and  of  the  Sahara — are  also  monsoons  on  a 
minor  scale. 

Land  and  sea  breezes,  as  they  are  called,  arise  from  similar 
causes,  and  might  be  termed  daily  monsoons.  They  occur  in  the 
warmer  regions  of  the  globe,  on  coasts  where  the  temperature  over 
the  land  is  much  higher  by  day  than  it  is  by  night,  while  over  the 
sea  it  remains  fairly  uniform.  As  the  sun  becomes  powerful,  the 
air  above  the  land  is  heated  by  radiation,  a  draught,  as  already 
described,  is  created,  and  a  breeze  sets  in  from  the  sea.f  This  falls 
gradually  at  the  approach  of  night.  For  a  time  the  air  is  still,  but 
at  a  later  hour,  when  the  land  has  been  chilled  by  radiation,  and 
the  air  above  it  has  become  colder  than  that  over  the  sea,  a  current 
is  created  in  the  opposite  direction,  and  the  land  breeze  springs 
up,  dying  away  as  the  day  is  dawning. 

Local  disturbances  are  produced  by  mountains,  for  each  peak  is 
like  an  island  in  the  surrounding  shell  of  atmosphere.  It  absorbs 
and  radiates  heat  at  a  different  rate,  and  acts  in  regard  to  the  air  as 
the  land  does  to  the  sea.  During  the  day  the  rocks  are  heated 
and  a  draught  is  created  toward  them.  During  the  night  they 
become  very  cold,  so  that  the  surrounding  air  is  chilled  and  flows 
downward.:]:  The  mistral,  the  abomination  of  visitors  to  the 


*  The  disturbance  affects  a  very  large  area  in  Northern  Africa,  extending  as  far  as  the 
Sahara.  (See  Reclus,  "  The  Ocean,"  ch.  vi.) 

f  The  sea  breeze  begins  about  10  A.M.,  is  strongest  about  3  P.M.,  and  is  replaced  by  a 
land  breeze  about  8  P.M. — Ferrel,  "  Popular  Treatise  on  the  Winds,"  p.  221. 

\  According  to  General  Strachey,  these  winds  are  very  marked  in  the  Himalayas,  where 
they  blow  up  the  valleys  from  about  9  A.M.  to  9  P.M. — Ferrel,  "  Popular  Treatise  on  the 
Winds,"  p.  22. 


34  THE   STORY  OF  OUR  PLANET. 

pleasant  regions  of  the  Riviera,  is  a  similar  but  still  more  marked 
instance.  This  is  a  bitter  northwesterly  wind,  which  descends  in 
winter  and  early  spring  from  the  cold  summits  of  the  Cevennes  and 
of  the  Maritime  Alps,  on  to  the  lowlands  of  Provence  and  the  coast 
of  the  Mediterranean.  But  France  and  the  adjoining  parts  of  Italy 
do  not  suffer  alone;  the  Adriatic  has  its  Bora,  the  Grecian  Archi- 
pelago its  Tramontana  Negra  or  "Black  Norther,"  for  these  winds 
are  due  not  only  to  the  neighboring  mountain  districts,  but  also  to 
the  fact  that  at  this  season  the  barometric  pressure  is  usually  high 
over  a  belt  extending  from  the  Spanish  peninsula  across  Europe 
to  the  interior  of  Asia. 

Lastly,  the  winds  inconstant  in  direction  and  sometimes  violent  in 
character  must  be  noticed.  The  ordinary  winds  and  their  changes 
result  from  inequalities  of  barometric  pressure,  which,  as  already 
mentioned,  depend  mainly  upon  differences  of  temperature  at  differ- 
ent parts  of  the  earth's  surface,  and  on  the  variable  amount  of 
aqueous  vapor  present  in  the  atmosphere.  The  air  over  a  district 
colder  than  the  surrounding  region  contracts.  If,  then,  the  atmos- 
phere be  regarded  as  divided  up  into  a  series  of  zones  or  shells,  of 
uniform  density,  a  slight  indentation  must  be  produced  in  each  one 
of  these  above  the  colder  area.  Into  this  the  surrounding  air 
would  flow,  like  water  into  a  saucer  the  edge  of  which  was 
depressed  just  below  its  surface,  so  that  a  larger  quantity  of  air 
ultimately  would  be  resting  over  this  colder  region.  Thus  the 
atmospheric  pressure  must  be  increased,  and  the  barometer  must 
rise.  But  when  once  this  inequality  of  pressure  was  established, 
the  air  would  naturally  tend  to  flow  away  from  the  region  of  the 
high  barometer  toward  the  region  of  the  low  barometer  till  equi- 
librium had  been  restored. 

In  like  way  the  heating  of  any  portion  of  the  earth's  surface 
raises  the  temperature  of  the  air  above  it,  and  produces  a  contrary 
effect,  the  barometer  falls,  and  then  an  inflow  is  set  up.  But  here 
also,  as  in  the  case  of  the  trade  winds,  the  rotation  of  the  earth 
modifies  the  motion  of  the  air.  In  the  northern  hemisphere  that 
which  is  flowing  southward  to  the  center  of  a  region  where  the 
barometer  is  low,  moves  also  in  a  westerly  direction,  while  that 
coming  from  the  south  is  deflected  eastward.  Thus  a  rotatory 
motion  is  impressed  upon  the  great  body  of  air  surrounding  the 
depression,  and  a  "cyclone"  is  the  consequence.  It  rotates  obvi- 
ously in  a  direction  opposite  to  that  of  the  hands  of  a  watch.  But 
the  contrary  effect  is  produced  in  the  case  of  an  outflow  from  a 


THE  AIR  REGION.  35 

region  of  high  pressure,  so  that  an  anti-cyclone,  as  this  wind  system 
is  called,  rotates  with  the  hands  of  a  watch.  This  rule,  however, 
only  holds  for  the  northern  hemisphere ;  in  the  southern,  obviously, 
the  reverse  process  must  occur,  so  that  its  cyclones  rotate  in  the 
same  direction  as  the  northern  anti-cyclones,  and  vice  versa.  The 
rate  at  which  the  air  moves  depends  largely  upon  the  nature  of  the 
change  in  the  level  of  the  barometer;  a  steep  gradient*  in  the  read- 
ings will  be  associated  with  a  rapid  current  of  air  or  strong  winds, 
a  low  gradient  with  gentle  breezes.  Steep  gradients  are  commoner 
around  areas  of  low  than  of  high  pressure,  so  that  the  former  more 
frequently  give  rise  to  storms.  The  relations  of  the  direction  of 
the  wind  and  the  height  of  the  barometer  in  the  northern  hemi- 
sphere are  stated  in  the  so-called  law,  named  after  Buys  Ballot,  by 
whom  it  was  first  enunciated.  It  runs  thus:  "Stand  with  your 
back  to  the  wind,  and  the  barometer  will  be  lower  on  your  left 
hand  than  on  your  right. "f  In  the  southern  hemisphere,  as  a  mo- 
ment's consideration  will  show,  "right"  and  "left"  must  be  reversed. 
The  annexed  copy  (Fig.  16)  of  one  of  the  daily  charts  issued  by 
the  Meteorological  Office  presents,  in  a  form  more  readily  intelligible 
than  words,  the  relation  between  the  height  of  the  barometer  and 
the  direction  of  the  wind.  The  curved  lines  show  the  "isobars,"  or 
lines  of  equal  pressure,  the  lowest  not  exceeding  28.6,  the  highest 
recorded  being  30  inches.  The  arrows  indicate  the  direction 
toward  which  the  wind  is  blowing.  Over  Wales  lies  a  low  pressure 
area,  roughly  circular  in  form,  the  center  of  which  probably  is  not 
far  from  Dolgelly.  The  isobars  over  the  greater  part  of  the  British 
Isles  form  closed  curves,  fairly  symmetrical  in  outline.  The  arrows 
show  that  the  air  over  the  same  area  is  circling  round  the  center 
spot  in  the  reverse  direction  to  that  of  the  hands  of  a  watch.  Over 
the  southern  parts  of  England  westerly  winds  prevail ;  along  the 
eastern  coasts  they  are  blowing  from  the  south;  in  the  northeastern 
districts  they  come  from  the  southeast,  and  in  the  northern  coun- 
ties they  have  changed  into  east  winds.  Finally,  over  Ireland  and 
the  intervening  Channel  they  become  successively  northeast,  north, 
and  northwest.  If  we  follow  the  isobars  over  Europe  toward  the 
south,  southeast,  and  east,  we  see  that,  so  far  as  the  chart  goes,  the 
same  rule  holds  generally,  though  some  slight  abnormality  may  be 
noticed  in  the  direction  of  the  wind  over  the  southeastern  part  of 

*So  called,  because  if  the  readings  were  plotted  on  a  curve,  this  would  slope  steeply, 
f  R.  H.  Scott,  "  Weather  Charts  and  Storm  Warnings,"  p.  23. 


36  THE   STORY  OF  OUR  PLANET. 

France,  which  may  be  due  either  to  the  proximity  of  the  Alps  or 
to  some  disturbing  cause  outside  the  limit  of  the  chart,  but  of 
which  the  widening  of  the  isobars  near  the  southeast  corner  may 
possibly  give  a  hint.  Toward  the  northeast  of  the  chart  the  isobars 
open  out,  influenced,  no  doubt,  by  a  high  pressure  area  lying  over 


FIG.  16.— CHART  OF  A  CYCLONIC  DISTURBANCE  OVER  THE  BRITISH  ISLES. 

Scandinavia  and  part  of  Northern  Europe;  but  as  it  affects  only  a 
small  portion  of  the  region  covered  by  the  chart,  and  the  gradients 
here  obviously  are  not  so  steep,  it  does  not  seem  to  produce  any 
marked  effect  upon  the  winds. 

Sometimes,  more  especially  in  the  case  of  an  anti-cyclone,  the 
center  of  the  system  may  remain  practi  ally  motionless  for  several 
hours,  or  even  for  some  days,  but  more  commonly  it  moves  over 
the  earth's  surface.  If  the  area  of  approximately  uniform  tempera- 


THE  AIR  REGION.  37 

ture  and  the  corresponding  circulatory  system  be  large,  the  winds 
will  be  steady  in  direction,  and  for  some  time  will  seem  to  follow  a 
rectilinear  course;  the  smaller  the  area  and  the  steeper  the  gradient 
the  more  readily  the  cyclonic  motion  will  be  detected.  In  the 
British  Isles,  as  everyone  knows,  the  easterly  winds  in  the  winter 
and  spring  are  dry,  cold,  and  often  steady  in  direction  for  many 
days.  The  reason  of  this  becomes  plain  when  a  set  of  charts  is 
studied  on  which  the  isotherms  for  this  part  of  the  year  have  been 
laid  down.  It  is  then  seen  at  once  that  Northern  Russia  is  a  very 
cold  region.  The  January  temperature  of  a  large  part  of  Russia, 
with  the  Northeast  of  Scandinavia  and  the  head  of  the  Baltic,  is 
below  14°  F. ;  at  Archangel  it  is  5°  F. ;  while  at  the  Land's  End 
and  in  Kerry  it  is  41°.  Between  the  temperature  of  the  western 
frontier  of  Russia  and  the  east  coast  of  England  there  is  a  differ- 
ence of  about  15°;  while  in  July,  for  the  same  latitude,  the  tem- 
perature in  Russia  is  slightly  higher  than  in  England.  In  the.  one 
case  there  is  a  great  fall  of  temperature  in  going  eastward,  in  the 
other  a  slight  rise ;  so  that  all  through  the  winter  and  spring  both 
Northeastern  Europe,  and  a  still  larger  area  of  Asia,  have  a  tempera- 
ture much  below  that  of  these  islands.  Hence  if  no  disturbing 
causes  interfere  a  draught  of  cold  air  must  be  set  up  by  this  vast 
refrigerator,  which  strikes  on  the  eastern  shores  of  Britain  with  its 
keenness  hardly  blunted  by  the  narrow  interval  of  sea.  But  strong 
gales  and  rainstorms  more  commonly  come  from  the  west,  being 
generally  the  result  of  cyclonic  disturbances  approaching  from  that 
quarter;  and  their  centers,  for  reasons  presently  to  be  considered, 
commonly  pass  to  the  north  of  these  islands.  Such  a  disturbance, 
therefore,  will  begin  with  a  gale  from  the  southwest,*  which  will 
"veer"f  by  the  west,  and  pass  away  by  the  northwest.  As  the  air 
has  been  traveling  over  the  Atlantic,  it  is  both  warm  and  laden 
with  moisture.  If,  however,  a  depression  passes  to  the  south  of  these 
islands,  the  wind  begins  from  the  southeast  and  "backs"  through 
the  east  to  the  northeast.  Such  winds,  as  will  be  presently  seen, 
are  usually:}:  less  violent  than  those  belonging  to  the  other  system. 
When  the  gradients  are  extremely  steep,  and  the  velocity  both  of 

*  Sometimes  the  first  symptom  of  the  approach  of  a  cyclonic  disturbance  is  a  wind  from 
an  easterly  quarter,  due,  apparently,  to  a  sort  of  "  insuck  "  of  the  air. 

f  The  wind  "veers"  when  it  changes  with  the  sun — viz.,  in  this  order:  east,  south, 
west,  north  ;  it  "  backs  "  when  the  change  is  in  a  contrary  direction — viz.,  from  the  east 
by  the  north. 

\  But  not  always,  e.g.,  January  18,  1881, 

431684 


38  THE   STORY  OF   OUR  PLANET. 

rotation  and  translation  is  very  rapid,  the  result  is  a  cyclone  (in  the 
popular  sense  of  the  term),  typhoon,  or  hurricane.  In  the  British 
Islands  these  visitations  are  comparatively  unknown ;  their  full  ter- 
rors are  displayed  in  tropical  regions.  But  a  tiny  tornado  can  be 
seen  on  almost  any  hot  summer  day,  when  little  columns  of  dust, 
only  a  few  inches  in  diameter  and  a  yard  or  so  in  height,  run  spin- 
ning along  the  highway.  Sometimes,  however,  they  get  bigger, 
and,  like  growing  children,  try  their  hands  at  a  little  mischief:  they 
whisk  some  haycocks  into  the  air,  .and  distribute  them  over  the 
next  field;  they  snap  off  or  uproot  a  tree;  they  unroof  a  shed,  or 
even  blow  down  a  wall.  One  Sunday  morning,  some  years  since, 
such  a  storm  was  seen  traveling  along  the  level  fields  three  or  four 
miles  away  from  Cambridge — a  moving  "pillar  of  cloud,"  dark  with 
whirling  dust  and  leaves  and  boughs,  not  many  yards  in  diameter. 
On  its  course  it  met  with  a  clump  of  poplars.  Some  of  the  trees  it 
snapped  off  short ;  others  it  split  in  two  or  three  places,  as  a  twig 
can  be  split  by  twisting  it  round ;  and  it  considerably  interfered 
with  the  order  of  a  Sunday  school  by  entering  in  through  the  door 
at  one  end  of  the  building  and  departing  at  the  other  by  blowing 
out  part  of  the  wall,  fortunately  without  injury  to  anyone.  On  the 
Continent  these  tornadoes  are  sometimes  more  formidable.  The 
path  of  one  which  passed  over  the  Italian  Tyrol  on  July  18,  1880, 
could  be  traced  for  many  miles,  though  at  intervals  nothing  was 
harmed.  This  indicated  that  the  whirlwind,  as  it  were,  "jumped" 
from  place  to  place,  the  center  of  cone-like  disturbance  rising  and 
falling,  as  may  be  seen  in  the  eddies  caused  by  an  obstacle  to  the 
current  of  a  rapid  river.  In  the  town  of  Botzen,  for  example,  little 
harm  was  done.  Clouds  of  dust  were  raised  up  higher  than  the 
cathedral  spire,  shutters  were  banged,  windows  occasionally  were 
smashed,  tiles  came  clattering  down  from  the  roofs;  and  if  Tyro- 
lese  chimneys  had  been  fitted  with  pots  of  the  English  pattern, 
probably  many  of  them  would  have  strewn  the  streets  with  sherds. 
In  the  pine  woods,  however,  the  whirlwind  had  often  done  not  a 
little  mischief.  It  had  uprooted  the  tall  firs,  sometimes  only  for  a 
space  of  a  rood  or  two,  but  sometimes  it  had  cleared  a  broad  path 
even  for  hundreds  of  yards  through  the  forest.  Often  the  trunks 
of  the  fallen  trees  were  flung  one  upon  the  other  like  a  heap  of 
gigantic  spilikins.*  Then,  suddenly,  the  clearing  came  to  an  end, 
so  that  for  a  considerable  distance,  not  a  tree  was  injured. 

*  The  firs  in  this  region  have  shorter  branches  and  proportionately  taller  boles  than 
those  of  the  other  parts  of  the  Alps. 


THE  AIR  REGION.  39 

Still  larger  and  more  formidable  whirlwinds  occur  in  North 
America.  "In  its  path  over  the  surface,  the  circling  movement  of 
the  writhing  air  and  the  sucking  action  of  the  partial  vacuum  in  the 
center  portion  of  the  shaft  combine  to  bring  about  an  extreme 
devastation.  On  the  outside  of  the  whirl  the  air,  which  rushes  in  a 
circling  path  toward  the  vortex,  overturns  all  movable  objects,  and 
in  the  center  these  objects,  if  they  are  not  too  heavy,  are  sucked  up 
as  by  a  great  air  pump.  Thus  the  roofs  of  houses,  bodies  of  men  and 
animals,  may  be  lifted  to  great  elevations,  until  they  are  tossed  by 
the  tumultuous  movements  beyond  the  limits  of  the  ascending  cur- 
rent and  fall  back  upon  the  earth.  When  the  center  of  the  whirl- 
wind passes  over  a  building,  the  sudden  decrease  in  the  pressure  of 
the  outer  air  often  causes  the  atmosphere  which  is  contained  within 
the  walls  suddenly  to  press  against  the  sides  of  the  structure,  so 
that  these  sides  are  quickly  driven  outward,  as  by  a  charge  of  gun- 
powder."* Houses  are  wrecked,  trees  uprooted,  trains  blown  over, 
bridges  destroyed,  roads  blocked  with  debris.  In  ten  years  between 
one  and  two  thousand  persons  were  injured  or  killed  in  the  West- 
ern States  of  America.  Details  of  the  effects  of  several  tornadoes 
are  quoted  by  Professor  Ferrel. 

The  following  extract,f  describing  a  tornado  at  St.  Cloud  and 
Sauk  Rapids,  Minn.,  on  April  14,  1886,  gives  an  idea  of  their  general 
character: 

"The  tornado  struck  the  Mississippi  River  at  a  point  opposite  to 
the  village  of  Sauk  Rapids,  and  fishermen  who  were  in  full  view  of 
the  crossing  aver  that  for  a  few  moments  the  bed  of  the  river  was 
swept  dry;  and  in  corroboration  of  this  remarkable  statement  they 
showed  me  a  marshy  spot  where  no  water  had  been  before  this  event 
took  place.  Two  spans  were  torn  away  from  the  substantial  wagon 
bridge  below  the  rapids,  one  span  being  hurled  up  stream  and  the 
other  down  it  by  the  rotatory  motion  of  the  blast,  great  blocks  of 
granite  being  also  torn  bodily  out  from  the  piers.  The  large  flour 
mill  near  the  bridge  was  leveled.  The  depot  of  the  Northern-Pacific 
Railroad  was  demolished,  and  the  central  portion  of  the  village  itself 
was  attacked  with  the  greatest  violence.  Being  the  county  seat,  the 
court  house  was  located  here,  a  substantial  structure,  of  which  only 
the  vault,  six  iron  safes,  and  the  calaboose  were  left— the  latter 
turned  upside  down.  A  fine  new  schoolhouse,  costing  $15,000,  was 


*  Shaler,  "  Aspects  of  the  Earth,"  p.  239. 
f  "  Popular  Treatise  on  the  Winds,"  p.  385. 


40  THE   STORY  OF  OUR  PLACET. 

completely  swept  away.  The  Episcopal  Church  was  so  utterly 
ruined  that  the  sole  relic  thus  far  found  is  a  battered  communion 
plate.  The  floor  of  the  skating  rink  is  all  that  is  left  of  that  struc- 
ture. Stores,  hotels,  a  brewery,  and  four-fifths  of  the  residences  in 
the  village  were  scattered  as  rubbish  along  the  hillsides  or -borne 
away  for  miles  through  the  air." 

About   thirty-nine  persons  were  killed  and   one  hundred  injured 


FIG.  17.— A  TORNADO,  FROM  A  PHOTOGRAPH. 

The  cloud  around  the  base  of  the  actual  tornado  indicates  the  dust  and  general  disturbance  produced 
by  its  passage. 

on  this  occasion.  In  other  accounts  we  read  of  a  large  gate  being 
carried  to  a  distance  of  200  feet;  a  heavy  lumber  wagon  "lifted  up 
bodily  and  carried  to  the  S.E.  over  a  cornfield  to  a  distance  of  100 
feet,  without  injury."  A  heavy  "sulky  cultivator,"  weighing  about 
600  pounds,  was  carried  free  from  the  ground  a  distance  of  86  yards 
to  the  S.S.E.,  and  broken  by  the  fall.  A  ten-gallon  keg  was  hurled 
about  40  rods,  and  a  large  iron-bound  trunk,  fitted  with  an  extra 
heavy  lock,  was  shattered  to  pieces  and  the  lock  found  half  a  mile 
to  the  N.E.  sticking  into  a  rail;  feather  beds  were  torn  to  strips 
and  their  contents  scattered  broadcast,  and  articles  of  clothing  were 
carried  for  four  or  five  miles. 

A  hurricane  in  the  West  Indies,  a  typhoon  in  the  Chinese  or 
Indian  seas,  a  cyclone  or  cyclonic  storm,  are  all  examples  of  atmos- 
pheric disturbances  of  a  similar  kind,  on  a  larger,  though  not  quite 
so  violent,  scale.  As  a  general  rule,  the  paroxysmal  character  of 
the  disturbance  is  diminished  as  the  area  affected  broadens;  the 
height  of  the  mass  of  air  affected  does  not  increase  in  proportion ; 
the  sucking  motion  at  the  center  disappears,  and  is  replaced  by 
comparative  calm.  In  these  hurricanes  two  features  obviously  call 


THE  AIR  REGION.  41 

for  an  explanation :  one  is  the  rotation — at  any  rate,  in  the  case  of 
storms  affecting  small  areas — the  other  the  motion  of  translation. 
Each  presents  difficulties;  for  each  more  than  one  explanation  has 
been  advanced.  One  thing  is  fairly  certain — namely,  that  the  influ- 
ence of  even  the  larger  hurricanes  does  not  extend  to  a  very  great 
distance  vertically  from  the  surface  of  the  earth,*  a  remark  which 
is  true  of  most  aerial  disturbances  of  a  local  character.  Glimpses 
of  clouds,  floating  in  comparative  calm  high  above  the  earth's  sur- 
face, may  be  sometimes  caught  through  the  whirling  rack  of  hurri- 
cane. Hence  it  seems  more  probable,  although  some  have  main- 
tained a  contrary  opinion,  that  hurricanes,  as  a  rule,  originate  in 
the  lower  regions  of  the  atmosphere.  Even  if  this  view  be  adopted, 
a  further  diversity  of  opinion  is  found  to  exist.  One  party  main- 
tains that  every  cyclone,  large  or  small,  is  generated  by  the  action 
of  two  air  currents,  opposite  in  direction,  their  lines  of  motion 
forming  tangents  to  the  initial  curve  of  rotation.  The  other  party 
holds  cyclones  to  be  due  primarily  to  differences  of  atmospheric 
temperature,  and  to  be  produced  as  follows:  In  an  arid  region,  such 
as  are  some  parts  of  the  United  States,  the  surface  of  the  earth  is 
greatly  heated  by  the  summer  sun ;  by  radiation  from  it  the  air 
immediately  above  is  warmed,  and  so  becomes  lighter  than  the 
colder  layers  higher  up.  Usually  the  one  will  rise,  the  other  will 
descend ;  but  it  may  occasionally  happen,  if  no  further  disturbing 
conditions  exist,  that  a  heavier  layer  may  be  floating  for  a  time 
upon  one  that  is  lighter.  Such  a  state  of  thoroughly  unstable 
equilibrium  will  be  ended  by  the  slightest  disturbance,  and  the 
result  will  be  catastrophic.  Some  writers  have  suggested  that  even 
the  tall  trunk  of  a  dead  tree  on  one  of  those  wide  inland  plains  may 
suffice  to  produce  an  upcast  draught  and  to  puncture,  as  it  were, 
the  upper  fluid,  and  thus  cause  a  downward  rush  through  the 
breach.  The  air  in  descending  acquires  a  rotatory  movement,  like 
water  in  flowing  through  the  escape  pipe  at  the  bottom  of  a  bath, 
and  the  unstable  condition  of  the  atmosphere  is  favorable  to  a 
rapid  extension  of  the  disturbance.  Such  storms,  to  which  the 
term  tornado  is  often  restricted,  seldom  affect  an  area  more  than 
about  500  feet  in  breadth  and  some  30  miles  in  length.  The 
cyclones  proper  may  have  a  width  of  from  200  to  500  miles,  though 
the  velocity  of  the  wind  varies  greatly  at  different  parts  of  the  area 


*  The  vertical  height  of  an  Indian  hurricane  seldom  much  exceeds  10,000  feet,  and  often 
is  not  much  more  than  5000  feet,  above  sea  level. 


SfOAY  OF  OUR  PLANET. 


disturbed,  while  the  length  of  their  course  may  also  be  proportion- 
ately greater. 

The  eye  or  center  of  the  storm  is  a  comparatively  calm  spot, 
about  which  the  wind  first  increases,  then  decreases  in  velocity. 
This,  however,  is  by  no  means  uniform  at  equal  distances  from  the 
center,  for  another  factor  has  to  be  taken  into  consideration.  The 
eye  of  the  storm  does  not  remain  at  rest,  but  moves  rapidly,  its 
velocity  sometimes  exceeding  a  hundred  miles  an  hour.  Suppose 


°r.erinu.da. 


FIG.  18.— THE  COURSE  OF  A  TORNADO  IN  THE  WEST  INDIES,  1868. 


The  figures  show  the  air  pressure  in  millimeters  0765  =  30.118  in.;  71 
arrows  show  the  direction  of  the  wind  around  the  cent< 


z  27.953  in.)-    The  smaller 
:>£  the  storm. 


the  storm  be  traveling  from  west  to  east,  and  rotating  in  the  oppo- 
site direction  to  the  hands  of  a  watch,  the  velocity  of  the  wind 
in  the  southern  half  of  the  cyclone  will  be  greater  than  in  the 
northern,  for  at  the  one  extreme  the  velocity  of  translation  will  be 
added  to  that  of  rotation,  but  at  the  other  will  be  subtracted  from 
it.  This  may  make  all  the  difference  between  a  destructive  tempest 
and  a  moderate  breeze. 

Such  cyclones  seem  to  be  on  too  great  a  scale  to  be  originated 
by  a  cause  comparatively  local,  like  two  layers  of  air  in  unstable 
equilibrium.  That  they  usually  happen  at  the  season  when  the 
regular  winds  are  reversed  is  also  a  significant  fact.  Thus  of  365 
West  Indian  hurricanes  on  record  between  the  years  1493  and  1885, 
245  occurred  in  the  month  of  October,  when  the  sun  has  passed 
south  of  the  line,  and  the  increasing  heat  of  the  South  American 


THE  AIR  KEG  ION.  43 

Coast  produces  a  flow  of  air  from  the  northern  continent  transverse 
to  the  ordinary  course  of  the  northeast  trade  wind.  In  the  Indian 
Ocean  also  cyclones  are  most  numerous  after  either  the  vernal  equi- 
nox or  the  great  heat  of  summer.  Thus  the  examination  of  a  list 
of  the  hurricanes  in  the  southern  hemisphere  has  shown  that  not  one 
of  them  occurred  in  July  and  August,  and  more  than  three-fifths 
raged  during  the  first  three  months  of  the  year. 

In  the  northern  hemisphere  a  cylone  generated  near  the  West 
Indies  first  travels  toward  the  N.W.,  then  it  turns  back  to  follow 
the  general  direction  of  the  coast  line  of  the  United  States,  and, 
lastly,  blows  itself  out  in  a  N.E.  or  N.N.E.  direction.  In  the 
southern  hemisphere  the  disturbance  originates  in  the  Indian 
Ocean,  not  far  from  the  equator,  to  the  south  of  Ceylon,  and  moves 
in  a  S.W.  direction  toward  the  islands  of -Reunion,  Mauritius,  and 
Madagascar,  whence  it  turns  away  to  the  S.E.,  and  expires  before 
it  reaches  the  Antarctic  seas.  In  each  case  the  curvature  of  the 
path  is  probably  due  to  the  same  cause — the  earlier  part  being  the 
result  of  the  resistance  of  the  trade  wind ;  the  later,  after  the 
storm  has  escaped  from  this  influence,  to  its  "overrunning  the  lati- 
tudes," as  happens  with  the  counter-trades. 

In  close  connection  with  the  atmospheric  circulation  is  the  fall  of 
rain.  Both  are  due  to  the  same  primary  cause — solar  heat.  If  a 
little  water  be  spilt  on  the  pavement  when  the  sun  is  shining,  the 
flags  are  soon  dry  again — the  fluid  has  been  converted  into  vapor 
and  has  been  absorbed  by  the  atmosphere.  Air  at  a  given  tem- 
perature can  retain  a  certain  quantity  of  water  vapor.  It  is  then 
said  to  be  saturated.  If  its  temperature  be  lowered  it  is  no  longer 
capable  of  holding  the  same  amount,  so  the  vapor  is  condensed, 
at  first  in  tiny  droplets,  floating  in  the  air,  forming  clouds;  after- 
ward, when  these  increase  in  quantity  and  augment  in  size,  the 
water  descends  as  rain.  So  if  vapor-laden  air  rise  into  colder 
regions  of  the  atmosphere,  the  result  is  clouds  and  perhaps  rain. 
If,  however,  the  temperature  of  the  air  be  raised,  a  cloud,  "already 
formed,  will  disappear — it  passes  back  into  vapor  and  becomes 
invisible.  Thus  the  morning  mists  often  vanish  before  the  sun. 
The  amount  of  water  which  a  mass  of  air  can  contain  in  the  form 
of  vapor  depends  upon  the  temperature,  but  does  not  vary  with  it 
directly.  So  if  two  saturated  air  currents  at  different  temperatures 
mingle,  the  mixture  is  no  longer  able  to  contain  the  whole  of  the 
water  as  vapor,  and  some  of  it  is  condensed,  and  this  may  form  a 
cloud  or  may  be  precipitated  as  rain. 


44  THE  STORY  OF  OUR  PLANET. 

Fog,  mist,  and  cloud  do  not  essentially  differ,  and  are  only  dis- 
tinguished by  their  position.  When  vapor  is  condensed  immedi- 
ately above  the  surface  of  a  plain  or  of  the  sea,  it  is  called  a  fog. 
This  sometimes  forms  a  very  thin  layer.  It  may  cover  the 
meadows,  yet  the  trees  may  stand  up  clear  above  it  as  they  do  from 
the  water  in  a  flood.  A  vessel  might  be  passing  through  a  bank  so 
dense  as  to  render  invisible  a  rock  only  a  few  yards  ahead,  and  yet 
the  sun  might  be  shining  on  its  topsails.  Sea  fogs  are  commonly 
produced  by  the  mixture  of  a  warm  vapor-laden  current  with  a 
colder  one.  Thus  the  Atlantic  to  the  south  of  Newfoundland,  and 
off  the  coast  of  the  United  States,  is  sometimes  not  free  from  fogs 
for  days  together,  owing  to  the  warm  air  from  off  the  Gulf  Stream 
mingling  with  that  chilled  by  the  Arctic  current.  Mist  only  differs 
from  fog  in  being  less  local,  and  perhaps  more  elevated  in  position ; 
and  cloud  is  only  a  mist  regarded  from  the  outside.  In  a  moun- 
tain region  the  advance  of  a  cloud  over  the  slopes  may  be  often 
watched.  Occasionally  its  boundary  is  almost  as  sharply  defined 
as  that  of  a  jet  of  steam — it  comes  rolling  on,  as  if  it  were  alive, 
blotting  out  crag  and  pasture  as  it  advances,  till  it  envelops  the 
observer  in  a  white  mist. 

Perhaps  no  better  illustration  can  be  found  of  the  development  of 
a  cloud  than  is  supplied  by  the  "streamers"  which  sometimes  are 
attached  to  mountain  peaks.  From  the  crags  a  long  cloud  banner 
floats  to  leeward,  like  a  pennon  from  a  mast.  It  is  generated  thus: 
The  current  of  air  which  strikes  the  peak  contains  a  considerable 
amount  of  vapor,  though  it  is  not  yet  saturated.  It  is  chilled  by 
contact  with  the  rocks,  its  saturation  point  is  at  once  lowered,  and 
the  vapor  is  condensed  into  a  cloud ;  but  the  part  of  the  current 
thus  affected  bears  but  a  small  proportion  to  the  whole  mass  of  air, 
so  that,  as  the  two  flow  on,  the  temperature  of  the  colder  streak  is 
gradually  raised,  the  cloud  is  vaporized,  and  finally  disappears. 

The  forms  assumed  by  clouds  depend  upon  a  variety  of  causes, 
such  as  the  nature  of  the  air  currents,  the  action  of  wind,  and  that 
of  electricity.  The  steam  from  a  locomotive  engine  often  affords 
excellent  illustration  of  the  different  varieties.  For  a  short  dis- 
tance from  the  top  of  the  funnel  the  air  is  transparent ;  then  the 
vapor  condenses  into  the  heavy  mass  called  a  cumulus ;  this  if  the 
wind  be  blowing  hard  is  riven  into  cirrus.  But  if  the  engine  be 
standing  under  a  shed,  the  cumulus  floats  upward  till  it  forms  a 
stratus  beneath  the  roof,  and  this  locally,  by  the  fall  of  the  con- 
densing vapor  in  drops,  may  become  a  nimbus. 


THE  At  ft  REGION.  45 

• 

All  water,  whether  in  puddle,  pool,  lake,  brook,  or  river,  is  sub- 
ject to  loss  by  evaporation ;  but  the  ocean,  of  course,  is  the  great 
source  of  supply  for  the  rainfall  of  the  globe,  and  the  sun  is  the 
great  pumping-engine  by  which  its  waterworks  are  kept  in  action. 
The  earth  is  made  fertile  by  the  heat  of  the  sun  and  the  cold  of 
space;  without  these  it  would  not  be  even  habitable.  Were  it  not 
for  the  former  the  water  would  never  be  raised,  and  the  shores  of 
the  arid  lands  would  be  laved  in  mockery  by  the  useless  ocean ; 
were  it  not  for  the  latter  the  vapor  would  pass  away  by  diffusion 
into  space  till  at  last  there  would  be  no  more  sea,  for  the  water 
would  never  fall  back  upon  the  earth  as  rain,  and  thus  the  land 
would  be  no  less  desolate. 

Nature's  process  of  "rain  making"  is  fully  illustrated  by  the  usual 
course  of  a  day  in  a  tropical  island  during  the  rainy  or  summer  sea- 
son. The  sky  at  sunrise  is  clear;  presently  clouds  form,  and  by 
ten  o'clock  the  heavens  are  densely  covered.  Shortly  afterward 
rain  begins  to  fall,  and  before  noon  there  is  a  downpour.  About 
five  o'clock  the  weather  improves,  the  clouds  break,  after  which  the 
sky  clears  and  the  night  is  fine.  The  explanation  of  this  periodic 
change  is  not  difficult  to  find.  As  soon  as  the  sun  had  risen  to 
some  distance  above  the  horizon  the  ocean  began  to  give  off 
abundant  vapor,  which  was  carried  up  by  the  rising  current  of  air 
until  it  reached  colder  regions;  here  condensation  set  in,  followed 
by  precipitation.  But  as  the  sun  declined  toward  the  west  and  the 
day  became  cooler  evaporation  gradually  ceased,  the  supply  of 
vapor  was  cut  off,  and  by  degrees  the  sky  became  clear. 

The  amount  of  rain  precipitated  and  its  distribution  throughout 
the  year  depends  to  some  extent  upon  causes  more  or  less  local  in 
character,  but  the  following  laws  are  found  usually  to  hold : 

(1)  The  amount  of  rainfall  on  the  globe  decreases  from  the  equa- 
tor toward  the  poles. 

(2)  If  the  surface  of  a  continent  remains  nearly  at  the  same  level, 
the  rainfall  is  heaviest  on  the  coast,  and  decreases  inland. 

(3)  In  passing  from  plains  up  the  slopes  of  mountains  the  rainfall 
usually  increases;  but  if  the  chain  rise  to  a  sufficient  height,  pre- 
cipitation reaches  a  maximum,  after  which  it  diminishes. 

(4)  In  the  temperate  zones  of  the  globe  a  greater  amount  of  rain 
falls  on  the  western  coasts  of  large  masses  of  land  than  on  the 
eastern ;  but  in  the  tropics  the  rule  is  reversed. 

(5)  Certain  regions  have  their  rainy  seasons;  others  are  almost, 
or  even  quite,  rainless. 


46  THE  STORY  OF  OUR  PLANET. 

The  reasons  for  the  first  four  rules  may  be  briefly  summarized. 
The  heaviest  precipitation  takes  place  near  to  the  region  of 
greatest  evaporation — much  of  the  water  is  spilled  near  the  pump. 
As  changes  of  temperature  are  more  marked  over  land  than  over 
the  ocean,  a  coast  is  likely  to  be  a  zone  of  precipitation ;  but 
beyond  this  the  conditions  above  a  level  district  will  continue  to 
be  fairly  uniform,  and  further  precipitation  will  not  occur  till  the 
vapor  impinges  upon  a  colder  surface  or  is  forced  up  into  colder 
regions  of  the  atmosphere — in  other  words,  till  the  land  becomes 
distinctly  higher ;  so  as  the  mountains  rise  precipitation  increases, 
till  most  of  the  moisture  has  been  removed  from  the  air.  In  the 
more  temperate  regions  of  the  earth  the  rainfall  is  heavier  on  the 
western  coasts  because  winds  are  frequent  from  the  west  and  south- 
west in  connection  with  the  counter-trades.  These,  especially  if 
they  blow  from  the  latter  direction,  are  comparatively  warm  and 
moist;  while  those  from  the  east  and  northeast,  which  .impinge 
upon  eastern  coasts,  come  from  colder  regions,  and  thus  are  com- 
paratively dry.  Besides  this,  they  are  traveling  toward  a  warmer 
climate,  and  so  are  able  to  retain  whatever  moisture  they  may  have 
already  absorbed.  But  in  regions  nearer  to  the  equator  the  con- 
trary rule  holds.  Here  the  trade  winds  dominate,  which,  as  they 
blow  from  the  eastern  half  of  the  compass,  have  traveled  over  a 
large  expanse  of  ocean,  and  thus  have  become  charged  with  vapor. 

Excellent  illustrations  of  the  former  rule  are  afforded  by  the 
British  coasts.  The  rainfall  in  the  eastern  counties  ranges  from 
about  22  to  25  inches  per  annum,  but  on  the  western  coast  from  35 
to  40  inches,  or  even  more.  The  effect  of  hills  is  distinctly  indi- 
cated, even  in  the  comparatively  undulating  region  of  the  southeast 
of  England,  for  the  annual  rainfall  rises  from  26.13  at  Greenwich  to 
30.77  on  Salisbury  Plain.*  But  this  variation  becomes  yet  more 
marked  in  the  northwest  district.  At  Liverpool  the  rainfall  is 
about  35  inches;  at  Manchester  it  is  38.18  inches;  but  at  the 
waterworks  of  the  former  town,  near  Rivington  Pike,  it  is  54.7; 
and  at  those  of  the  latter,  near  Woodhead,  it  is  52.3.  So  that 
the  Lancashire  portion  of  the  Pennine  range,  which  reaches  a 
height  of  rather  more  than  a  thousand  feet  above  the  western  low- 
land, makes  a  difference  in  the  rainfall  of  from  14  to  18  inches. 
Further  north,  where  the  mountains  of  the  Lake  District  rise  nearer 
to  the  coast,  and  yet  more  abruptly,  the  difference  is  still  more 

*At  Chittenden  (from  information  communicate'd  by  R.  H.  Scott,  Esq.,  F.  R.  S.). 


THE  AIR  REGION.  47 

strongly  marked.  On  the  Cumberland  coast  the  rainfall  is  about 
35  inches,  but  at  the  head  of  Borrowdale  and  on  the  surrounding 
hills  it  is  commonly  not  less  than  150  inches,  and  during  wet  years 
is  even  more.  For  instance,  in  1872,  131.3  inches  was  measured  at 
VVasdale  Head,  186.25  inches  at  Seathwaite  in  Borrowdale,  and  as 
much  as  243.9  inches  on  the  Stye  Head  Pass,  between  the  two 
places.  Ben  Nevis  also  affords  a  good  illustration  of  the  effect  of  a 
western  coast  and  a  comparatively  high  mountain.  Fort  William  at 
its  base,  though  by  the  seashore,  is  at  the  head  of  a  long  inlet  which 
is  bordered  by  high  hills.  The  rainfall  accordingly  is  heavy,*  being 
77.33  inches;  but  at  the  observatory  on  the  summit  of  Ben  Nevis, 
4406  feet  above  the  sea,  the  corresponding  amount  is  129.47  inches. 
The  same  effect  is  produced  by  mountainous  districts  in  the 
interior  of  continents — for  instance,  in  the  wide  valley  of  the  Rhine, 
between  the  Black  Forest  and  the  Vosges,  the  rainfall  is  only  22  or 
23  inches;  but  on  the  higher  parts  of  the  latter  range  it  varies  from 
43  to  47  inches.  Again,  at  Geneva  it  is  about  32  inches;  at  the  St. 
Bernard  Hospice  it  amounts  to  79  inches. 

But  the  classic  instance — for  it  is  the  most  remarkable  on 
record— is  afforded  by  the  Khasia  Ghauts,  a  range  of  hills  rising 
above  the  great  alluvial  plains  of  the  Ganges,  in  front  of  the 
Bhootan  Himalayas,  to  a  height  of  from  4000  to  5000  feet  above 
the  sea,  and  separated  from  that  chain  by  the  valley  of  the  Brahma- 
pootra. South  of  the  delta  lie  the  steaming  waters  of  the  Indian 
Ocean,  from  which  the  saturated  air  at  the  period  of  the  monsoon 
travels  northward  toward  the  mountains.  On  the  delta  itself  the 
rainfall  is  considerable,  amounting  to  about  80  inches.  But  here 
the  aerial  current  merely  scatters  its  superfluous  moisture.  When 
it  strikes  upon  the  Ghauts,  the  height  of  which  probably  almost 
equals  the  depth  of  the  current,  the  precipitation  begins  in 
earnest,  and  the  rain  literally  streams  from  the  clouds.  At  Chira- 
poongi  a  fall  of  30  inches  in  twenty-four  hours  has  been  recorded  ;f 
the  annual  fall  commonly  exceeds  500  inches,  sometimes-  is  even 
more  than  600  inches,  and  most  of  this  is  precipitated  during  six 

*  This  is  heavy  in  another  sense,  for  the  total  weight  of  water  thus  precipitated  on  an 
acre  of  ground  is  approximately  7730  tons.  Could  all  of  it  be  collected,  the  water  that 
comes  down  on  each  square  mile  would  supply  a  city  containing  rather  more  than  100,000 
people,  at  an  allowance  of  thirty  gallons  per  head  per  day.  The  amount  annually  required 
by  1333  persons  is  equivalent  to  an  inch  of  water  on  a  square  mile. 

f  By  Dr.  (now  Sir  W.)  Hooker.  In  England  an  inch  in  the  same  time  is  thought  a 
rather  unusually  heavy  rain,  and  four  times  that  amount  is  not  often  reached,  and  very  rarely 
exceeded. 


48  THE   STORY  OF  OUR  PLANET. 

months  of  the  year.  The  Ghauts  plunder,  but  they  are  not  suffi- 
ciently lofty  to  exhaust,  the  aerial  current ;  it  overflows  their  sum- 
mits and  crosses  the  Brahmapootra  valley.  But  for  a  time  it  dis- 
charges no  more  rain — it  is  like  a  sponge  which  a  child  has  squeezed 
as  tightly  as  he  can ;  a  man's  grip  is  needed  before  it  will  yield 
more  moisture.  So  the  lower  slopes  of  the  Bhootan  Himalayas,  to 
a  height  of  some  5000  feet  above  the  sea,  are  arid.  But  this  chain 
towers  up  far  above  the  highest  summits  of  the  Ghauts;  so  the 
aerial  current  breaks  upon  that  mighty  rampart,  which  exacts  the 
"utmost  farthing"  of  moisture  as  the  price  of  passage;  hence  its 
higher  slopes  enjoy  a  fairly  abundant  rainfall,  and  are  clothed  with 
a  luxurious  vegetation. 

The  above  instance  has  afforded  an  example — though  on  a  small 
scale — of  a  rainless  district ;  but  there  are  extensive  regions,  some  of 
which  are  nearly,  others  entirely,  without  rain.  But  little  falls  over 
a  large  area  south  and  east  of  the  Caspian  Sea;  in  the  inland  coun- 
try of  South  Africa  or  Southern  Australia;  in  the  Arctic  regions  of 
America  and  Asia;  in  those  south  of  latitude  60°  in  the  opposite 
hemisphere;  in  the  cafion  country  of  Colorado  and  some  adjoining 
parts  of  the  United  States,  and  in  a  comparatively  small  district  of 
Western  Mexico.  The  last  receives  little  more  than  an  occasional 
shower,  but  there  are  other  regions  which  are  doomed  to  total 
abstinence.  These  are  three  in  number,  two  of  them  appearing  to 
be  rather  nearly  connected.  The  first,  and  smallest,  is  in  the 
southern  hemisphere,  on  the  western  slopes  of  the  Andes,  a  long 
and  narrow  strip  extending  for  about  30°  southward  from  latitude 
5°  S.,  through  Peru  and  part  of  Chili.  The  second  is  a  much  more 
extensive  region,  and  in  quite  another  part  of  the  globe.  It  is  a 
belt  of  land  about  10°  in  breadth,  which  begins  not  very  far  from 
the  west  coast  of  North  Africa,  and  extends  over  the  Sahara  and 
through  the  Libyan  Desert  to  the  other  side  of  the  continent,  cross- 
ing the  Red  Sea  into  Asia.  It  has  now  become  narrower,  and  so 
continues  across  the  North  of  Arabia  into  Persia,  where  it  termi- 
nates near  the  western  border  of  Afghanistan,  having  covered  about 
60°  of  longitude.  The  third  region  is  rather  narrower  and  less 
extensive,  for  it  begins  about  longitude  75*  E.  and  terminates 
in  longitude  115°,  including  part  of  Eastern  Turkestan  with  the 
Desert  of  Shamo  or  Gobi.  The  first  of  these  regions  lies  in  the 
zone  of  the  southern  trade  winds.  Thus,  though  the  Pacific  is  near 
to  it  on  the  west,  the  ocean  cannot  relieve  the  thirsty  land,  for  the 
air  currents  set  off  the  shore.  To  the  east  rises  the  lofty  chain  of 


THE  AIR  REGION.  49 

the  Andes,  and  beyond  this  is  the  whole  continent  of  South 
America,  so  that  all  supplies  from  that  quarter  are  effectually  inter- 
cepted. Somewhat  similar  causes,  though  rather  more  compli- 
cated, account  for  the  aridity  of  the  second  region.  Little  rain  can 
come  from  the  west,  for  the  air  currents  tend  to  flow  southward  and 
westward,  and  that  little  is  arrested  on  the  coasts.  For  the  reason 
just  given,  the  southern  quarter  would  not  in  any  case  avail  much, 
and  in  that  direction  lies,  at  first,  part  of  the  continent  of  Africa, 
afterward  almost  the  whole  of  Arabia.  The  Mediterranean  is  not  a 
sheet  of  water  sufficiently  extensive  to  furnish  a  large  supply  of 
moisture,  and  as  the  air  from  that  quarter  is  moving  southward, 
over  comparatively  low  ground,  there  is  nothing  to  cause  precipita- 
tion. The  desert  of  Gobi  is  guarded  on  two  sides  and  on  part  of  a 
third  by  lofty  mountain  chains.  These  effectually  desiccate  the  air 
which  may  cross  them.  For  the  remainder  of  the  northern  side 
the  ground  continues  fairly  high;  from  this  quarter  also  but  little 
moisture  could  ever  come,  while  from  the  eastern  seas  the  winds 
will  not  often  blow,  and  will  be  dried  before  they  have  passed  the 
Chingan  Mountains. 

Thus  the  whole  system  of  the  atmospheric  circulation  and  of  the 
rain  supply  is  extremely  complicated.  Dependent  primarily  on  the 
heat  of  the  sun  and  on  the  cold  of  space,  it  is  largely  affected  by 
secondary  causes,  such  as  the  distribution  of  land  and  water,  and 
the  configuration  of  the  terrestrial  surface.  Local  changes  may 
have  far-reaching  effects,  and  the  climate  of  any  region  may  be 
greatly  altered  by  important  modifications  in  the  outlines  of  the 
continents — that  is  to  say,  in  the  physical  geography  of  the  globe. 
The  present  is  not  a  stereotyped  repetition  of  the  past,  though  it 
supplies  the  materials  for  inference  and  induction.  The  land  which 
now  is  well  watered  once  may  have  been  arid ;  and  the  desert  of 
to-day,  where  the  sparse  bent  grass  withers  and  the  dust  storm 
whirls  over  the  dry  plains,  may  have  been  "a  place  of  broad  rivers 
and  streams,"  where  the  lowlands  were  green  with  lush  herbage, 
and  the  slopes  clothed  with  impenetrable  forests. 


CHAPTER  IV. 

THE   WATER   REGION. 

FULL  seven-tenths  of  the  earth's  surface,  as  has  been  already 
stated,  are  covered  by  water.  Every  river  may  be  said  to  have  its 
source  in  the  ocean  and  its  grave  in  a  sea.  Without  an  ocean  there 
would  be  no  vapor,  without  vapor  no  rain,  without  rain  no  streams. 
By  these  the  water  is  transferred  from  slope  to  slope,  from  hill  to 
valley;  here  it  may  wander  deviously  over  the  plain;  there  it  may 
stagnate  for  a  time  as  a  marsh  or  broaden  out  into  a  lake;  but, 
except  in  some  few  cases  where  its  contents  are  slowly  diminished 
by  evaporation  and  its  stream  is  dried  up  among  arid  sands,  every 
river  empties  itself  at  last  into  some  great  water  basin.  This  occa- 
sionally is  an  inland  sea — such  as  Lake  Baikal  or  the  Caspian  Sea — 
but  is  more  commonly  the  ocean. 

In  river  water  some  mineral  salts  are  present.  Of  these  parts 
may  be  removed  by  various  agencies  during  its  journey,  but  other 
constituents  remain,  and  are  concentrated  in  the  basin  in  which 
the  river  comes  to  an  end.  Thus  while  the  water  of  a  lake  through 
which  a  river  runs  is  fresh — *.  e.,  contains  an  imperceptibly  small 
proportion  of  certain  mineral  salts — that  of  an  inland  sea  and  of 
the  ocean  is  always  more  or  less  saline,  as  can  be  recognized  by  the 
taste  and  by  other  rough  tests. 


English 

Mcditer. 

Black 

Caspian 
Sea 

Great 
Salt  Lake 

Dead 

Channel. 

ran  can. 

Sea. 

(Baku). 

(Utah). 

Sea. 

Chloride  of  sodium 

2.7059 

2.9424 

1.4019 

8.5267 

11.8628 

3.6372 

potassium 

.0765 

.0505 

.0189 

(trace) 

.0862 

.8379 

magnesium     .  . 

.3666 

.3219 

.1304 

.3039 

I.490S 

15-9774 

"          lime 











4.7197 

Sulphate  of  magnesia 

.2295 

•2477 

.1470 

3-2493 





"           lime 

.1406 

•1357 

.OIO4 

I  0742 

.0858 

.0889 

"           soda 









.9321 



"           potash 









•53^3 



Carbonate  of  lime 

•0033 

.OII4 

.0364 

•0554 





"           magnesia 





.O2O8 







Bromide  of  magnesium   .  . 

.OO29 

•0556 

.OOO5 





.8157 

Water        

96.4747 

96.2348 

98.2337 

86.7905 

85.0060 

73.9232 

100 


IQO 


100 


THE    WATER  REGION.  51 

The  foregoing  table*  exhibits  the  amount  of  soluble  salts  present 
in  ocean  water.  For  purposes  of  comparison  analyses  of  the  water 
of  some  inland  seas  have  been  added. 

Slight  variations  are  noted  in  the  total  amount  of  the  salts  pres- 
ent in  ocean  water  at  different  times  of  the  year  and  in  different 
parts  of  the  world.  According  to  Dittmar  the  samples  collected 
during  the  voyage  of  the  Challenger  afforded  quantities  which 
varied  from  3.301  per  cent,  of  the  water  for  the  southern  part 
of  the  Indian  Ocean  to  3.737  for  the  North  Atlantic,  about  lati- 
tude 25°. 

The  following  table  gives  the  proportion  of  the  saline  constituents 
contained  in  an  average  sample  of  oceanic  water: 

Chloride  of  sodium  . .  . .  . .  .  .  77-758 

"  magnesium  . .  . .  .  .  .  .  10.878 

Sulphate  of  magnesia  ..  ..  ..  . .  4-737 

"           lime  . .  . .  .  .  .  .  3.600 

potash  .  .  .  .  . .  . .  2.465 

Bromide  of  magnesium  . .  . .  .  .  .  .  0.217 

Carbonate  of  lime  . .  . .  . .  . .  0.345 


But  in  addition  to  these,  many  other  elements  are  present  in  sea 
water,  though  generally  in  extremely  minute  proportions.  The 
gases  dissolved  have  been  estimated  as  ranging  in  amount  from  just 
below  two  to  just  above  three  per  cent.  These  are  oxygen,  nitrogen, 
and  free  carbonic  acid,  the  last  being  only  occasionally  present,  and 
always  in  very  small  quantities.  The  proportion  of  oxygen  is 
greatest  in  the  surface  water  and  least  in  that  at  the  bottom. 
Besides  these,  iodine,  fluorine,  phosphorus,  silicon,  barium,  may  be 
mentioned  among  others,  and  a  considerable  number  of  the  metals, 
including  such  ordinary  substances  as  iron,  copper,  lead,  manganese, 
silver,  and  gold,  and  such  rarities  as  caesium  and  rubidium.  In  fact, 
the  ocean  water  contains,  though  always  in  comparatively  small  and 
often  in  extremely  minute  quantities,  most  of  the  elements  which 
enter  into  the  composition  of  the  earth's  crust,  and  it  is  probable 
that  nearly  all  may  be  actually  present,  though  in  such  inconsider- 
able amounts  as  to  elude  the  investigator. 

Between  the  contours  of  the  land  and  those  of  the  adjacent 
ocean  bed,  as  a  general  rule,  a  certain  relation  may  be  observed. 

*  Compiled  from  Prestwich,  "Geology,"  pt  i,  ch.  vii.,  and  Geikie,  "Textbook  of 
Geology,"  book  iii.  part  ii.  sect.  ii.  §  4. 


52  THE   STORY  OF  OUR  PLANET. 

Both  alike  either  shelve  gently  or  descend  rapidly  downward  ;  but 
in  each  case  the  submarine  slope  is  less  steep  than  the  subaerial 
one.  Still,  occasionally,  abrupt  changes  of  level  have  been  noticed 
in  the  sea  bed,  as,  for  example,  off  the  Abrolhos,  when  on  one  side 
of  Captain  Fitzroy's  vessel  the  lead  descended  to  a  depth  of  4  to 
6  fathoms,  but  on  the  other  side  the  soundings  were  from  16 
to  22  fathoms.  As  this  locality  is  not  within  a  region  of  coral 
reefs,  so  marked  a  difference  can  only  be  explained  by  assum- 
ing the  existence  of  a  submarine  cliff.  Again,  the  ocean  floor  is 
found  in  some  cases  to  descend  from  the  margin  of  a  continent  or 
a  large  island  gradually  and  steadily  to  great  depths,  while  in  others 
this  downward  slope  does  not  really  begin  till  a  considerable  inter- 
val of  comparatively  shallow  water  has  been  traversed.  Thus  the 
bed  of  the  North  Atlantic  descends  with  fair  uniformity  from  the 
coast  of  the  Iberian  peninsula  and  the  nearest  parts  of  France  to  a 
depth  of  1000  fathoms,  which  is  found  about  forty  miles  away,  and 
for  a  considerable  distance  off  the  northwest  of  that  region  it 
reaches  2000  fathoms  at  about  double  this  interval ;  but  the  British 
Islands,  with  the  northern  parts  of  France,  rise  from  a  submarine 
plateau,  all  of  which  lies  within  the  contour  line  of  100  fathoms. 
A  vessel  does  not  pass  over  the  margin  of  this  plateau  until  it  has 
proceeded  about  five-and-thirty  miles  west  of  Valentia,  and  more 
than  two  hundred  miles  west  of  the  Land's  End.  Then  the  sea 
bed  begins  to  fall  much  more  rapidly,  and  slopes  down  at  an  angle 
of  about  eight  degrees  to  a  depth  of  full  2000  fathoms.  The  bed 
of  the  Atlantic  between  Europe  and  America  consists  of  two  broad 
troughs,  which  follow  roughly  the  coasts  of  the  respective  conti- 
nents, and  commonly  vary  in  depth  from  about  2000  to  2800 
fathoms.  These  are  separated  by  a  submarine  plateau,  also  of  con- 
siderable breadth,  which  supports  the  Azores,  and  seldom  rises 
more  than  some  1800  feet  above  the  2OOO-fathom  contour  line, 
except  in  the  immediate  neighborhood  of  these  islands.  This 
plateau  at  its  northern  end  is  united  to  another  one  which  runs 
transversely  from  the  British  Isles  to  Greenland.  The  course  of 
this  submerged  causeway  is  indicated  by  the  Shetland  Isles,  the 
Faroes,  and  Iceland,  a  large  part  of  it  is  well  within  the  5oo-fathom 
contour  line,  and  its  greatest  depth  does  not  exceed  about  600 
fathoms. 

The  two  basins  mentioned  above  deepen  gradually  to  the  south ; 
the  intervening  plateau  also  sinks,  though  it  continues  to  form  a 
distinctive  feature  in  the  general  contour  of  the  ocean  floor. 


50  ta  100  Ftthtmt  CMC  TOO  Ftthtmi 

FIG.  19. — MAP  OF  NORTHWESTERN  EUROPE,  WITH  THE  SUBMARINE  CONTOURS. 


54  '  THE    STORY  OF  OUR  PLANET. 

(Plate  I.)  At  last,  between  latitudes  10°  and  23°  N.,  a  part  of  the 
eastern  basin,  somewhat  triangular  in  form,  with  one  side  following 
the  general  contour  of  the  African  coast,  attains  a  depth  of  over 
3000  fathoms.  The  western  basin  also  shelves  down  to  a  depres- 
sion which,  however,  is  even  larger  and  deeper.  This  in  shape 
roughly  resembles  the  letter  C,  and  it  extends  from  about  latitude 
35°  N.  to  14°  N.,  the  back,  as  it  were,  following  the  general  contour 
of  the  American  coast,  and  resting  on  the  West  Indian  Isles.  In 
their  neighborhood,  at  no  great  distance  from  the  island  of  St. 
Thomas,  soundings  of  3875  fathoms  have  been  obtained,  the 
greatest  depth  known  in  the  North  Atlantic.  The  intervening  sub- 
marine plateau,  already  mentioned,  is  prolonged  to  and  across  the 
equator,  but  it  throws  off  one  spur  which  runs  westward,  at  a  gen- 
eral depth  of  from  1500  to  2000  fathoms,  to  the  coast  of  South 
America,  north  of  the  mouth  of  the  Amazon,  and  another  which 
runs  eastward  to  the  African  coast.  Its  general  course  beneath  the 
water  is  marked  by  the  islands  of  St.  Paul,  Ascension,  and  St. 
Helena — volcanic  masses  which,  like  beacons  on  a  reef,  indicate  the 
presence  of  this  great  inequality  in  the  ocean  floor.  Then  the 
bed  of  the  Atlantic  Ocean,  as  a  whole,  rises  toward  the  south, 
mounting  up  to  the  icy  land  which  encircles  the  southern  pole. 
Thus  the  Antarctic  continent  is  surrounded  for  a  considerable 
distance  by  a  sea  which  deepens  very  gradually  for  the  first  thou- 
sand fathoms. 

The  submarine  contours  of  the  Pacific  Ocean  (Plate  II.)  are  more 
difficult  to  describe.  It  is  deeper  on  the  whole  than  the  Atlantic, 
though  its  surface  is  far  more  broken  by  islands,  which,  however, 
do  not  very  materially  reduce  the  average  soundings,  but  rise  up 
rather  abruptly  from  great  depths.  The  basins  also  are  less  closely 
related  in  their  distribution  to  the  coasts  of  the  greater  continents. 
A  comparatively  shallow  plateau  unites  the  Japanese  Islands  to 
Asia,  and  that  continent  to  America.  A  rise  of  less  than  50 
fathoms  would  replace  Behring's  Straits  by  dry  land,  and  convert 
the  Arctic  Ocean  into  a  mare  clausum.  Southward  from  this  sub- 
merged causeway  the  sea  bed  plunges  down  to  great  depths. 
Skirting  the  islands  of  the  N.E.  Asian  and  N.W.  American  coasts 
lies  the  so-called  Tuscarora  Deep — a  vast  area  below  the  3OOO-fathom 
contour  line.  In  this,  near  the  Kurile  Islands,  north  of  Japan,  a 
depth  of  4655  fathoms  was  measured.  To  the  south  of  this  deep  is 
a  considerable  area  over  which  the  soundings  are  from  2000  to  3000 
fathoms,  and  this  rises  gradually  to  a  long  plateau,  which  comes 


THE    WATER  REGION.  55 

within  the  2OOO-fathom  line,  extending  for  nearly  10°  west  of  the 
Sandwich  Islands.  South  of  this  area,  beneath  the  equator,  a  con- 
siderable tract  is  between  2000  and  3000  fathoms  deep,  but  it  is 
interrupted  by  sundry  small  groups  of  islands,  which,  however,  pro- 
duce comparatively  little  effect  upon  the  general  level  of  the  bed. 
A  very  broad  plateau,  seldom  more  than  100  fathoms  below  the 
surface,  but  interrupted  here  and  there  by  comparatively  small  yet 
rather  deep  basins,  links  Asia  with  the  Philippine  and  other  adja- 
cent islands,  and  these  with  the  Australasian  Islands  and  Australia. 
The  plateau  continues,  though  sinking  to  a  distinctly  greater 
depth — for  it  can  now  be  more  easily  traced  by  the  2OOO-fathom 
line — through  the  Solomon  and  Fiji  Islands.  Near  the  latter  it 
divides,  one  branch  taking  a  westerly  course  by  the  New  Hebrides 
toward  the  southern  part  of  Queensland,  and  thus  inclosing  the 
basin  of  the  Coral  Sea;  another  running  diagonally  to  New  Zea- 
land, and  thence,  in  a  northwesterly  direction,  toward  the  arm 
already  mentioned.  To  this  it  is  joined  rather  to  the  west  of  New 
Caledonia,  thus  inclosing  another  basin.  New  Zealand  is  parted 
from  New  South  Wales  by  a  broad  channel  over  2000  fathoms 
deep,  but  it  throws  out  submarine  spurs  toward  the  latter  and  the 
Antarctic  plateau,  which  is  reached  without  obtaining  any  sound- 
ings of  that  depth.  The  eastern  half  of  the  Pacific  presents  more 
uniform  contours,  it  is  almost  everywhere  considerably  below  the 
2ocx>fathom  contour  line,  and  not  seldom  approaches  3000 
fathoms,  but  from  the  coast  of  Chili  a  long  spur-like  plateau  passes 
beneath  Juan  Fernandez,  and  may  be  traced  as  far  as  Tahiti,  much 
of  it  being  less  than  1500  fathoms  beneath  the  surface.  An  isolated 
basin,  4475  fathoms,  was  found  by  the  Challenger  south  of  the 
Ladrone  Islands;  a  sounding  of  4530  fathoms  was  obtained  north 
of  the  Friendly  Islands,  and  one  of  4428  fathoms  south  of  them ; 
but  the  most  curiously  situated  hole  in  the  Pacific  forms  a  narrow 
trench,  nearly  4200  fathoms  deep,  off  the  coast  of  Chili,  north  of 
Coquimbo. 

The  Indian  Ocean  exhibits  greater  simplicity  in  the  contours  of 
its  bed.  It  has  an  average  depth  of  about  2500  fathoms,  reaching 
3000  in  the  deepest  part  between  Java  and  Northwestern  Australia, 
and  at  last  it  rises  gradually  southward  toward  the  Antarctic 
plateau  so  as  to  come  within  soundings  of  about  1000  fathoms  in 
the  neighborhood  of  latitude  40°.  From  this  plateau  rise  Ker- 
guelen,  Crozet,  and  Prince  Edward's  islands.  A  considerable  space 
in  the  Mozambique  Channel,  which  separates  Madagascar  from 


56  THE   STORY  OF  OUR  PLANET. 

Africa,  is  rather  deeper  than  1500  fathoms,  and  the  Seychelles  are 
somewhat  more  closely  related  to  that  island  than  to  the  continent. 
The  Mascarene  Islands,  however,  appear  to  be  fairly  distinct  from 
both,  since  the  plateau  from  which  they  rise  is  surrounded  by  water 
over  1500  fathoms,  though  it  is  most  in  connection  with  that  of  the 
Seychelles. 

The  description  given  above  indicates  that  the  land  masses  of  the 
globe  are  generally  most  nearly  linked  together  by  their  northern 
ends.  If  the  level  of  the  ocean  were  lowered  by  100  fathoms  only, 
as  already  stated,  it  might  be  possible  to  pass  dryshod  from  Aus- 
tralia to  Asia,  and  then  to  travel  by  the  latter  to  North  America, 
and  so  to  the  end  of  the  New  World's  continental  land.  A  com- 
plete circuit  of  the  globe  could  not  be  made  roughly  along  the  line 
of  the  Arctic  Circle,  for  open  water  would  still  remain  between 
Northwestern  Europe  and  Greenland,  but  the  depth  of  this  gener- 
ally would  be  comparatively  slight,  nowhere  amounting  to  1000 
fathoms,  while  the  Antarctic  plateau  is  everywhere  separated  from 
the  continental  masses  by  a  channel  of  at  least  this  depth. 

The  Mediterranean  Sea  is  not  only  a  basin  in  itself,  but  it  also 
consists  of  a  group  of  basins.  If  the  general  level  of  the  ocean 
were  lowered  by  200  fathoms,  the  Straits  of  Gibraltar  would  be 
closed  and  Europe  united  to  Africa  by  an  isthmus.  One-half  that 
amount  of  lowering  would  unite  Majorca  with  Minorca,  Sardinia 
with  Corsica,  Malta  with  Sicily;  and  by  closing  the  Straits  of 
Otranto  would  greatly  augment  the  area  of  Italy.  By  such  a 
change  almost  the  whole  of  the  Adriatic  would  become  dry  land ; 
the  Po  and  the  Adige,  the  rivers  of  the  Istrian  and  Dalmatian  coast, 
and  of  the  Eastern  Apennines,  would  all  flow  into  a  shallow  inland 
sea  north  of  the  Straits  of  Otranto.  The  Mediterranean  then 
would  be  almost  cut  in  two,  but  a  rise  of  rather  more  than  another 
hundred  fathoms  would  be  required  to  make  a  second  land  passage 
from  Africa  to  Europe,  for  soundings  of  240  fathoms  are  obtained 
in  a  narrow  channel  south  of  Malta.  The  submarine  area  inclosed 
between  this  region  and  the  Straits  of  Gibraltar  really  consists  of 
two  basins,  which  are  separated  by  a  plateau  starting  from  the 
Genoese  coast  and  prolonged  through  Corsica  and  Sardinia  south- 
ward to  Africa.  The  western  basin  is  1600  fathoms  deep;  the 
eastern,  which  is  rudely  triangular  in  form  and  smaller  in  area, 
attains  a  depth  of  2300  fathoms.  A  large  part  of  the  ^Egean  Sea 
is  within  the  loo-fathom  contour  line,  and  its  depth  nowhere 
exceeds  500  fathoms,  except  in  a  well-marked  basin  which  lies  off 


THE    WATER  REGION.  57 

the  northern  shore  of  Crete,  and  corresponds  generally  in  outline 
with  that  island.  A  rise  of  100  fathoms  would  put  an  end  to  the 
Eastern  Question  by  closing  both  the  Dardanelles  and  the  Bos- 
phorus,  and  so  converting  the  Black  Sea  into  another  Caspian.  It 
also  is  a  well-marked  basin,  the  greatest  depth  of  which  is  10/0 
fathoms;  and  even  the  Sea  of  Marmora  takes  the  same  peculiar 
form,  its  deepest  soundings  amounting  to  358  fathoms. 

Attention  may  be  called,  before  proceeding  further,  to  an  irregu- 
larity in  the  ocean  floor  which,  though  on  a  smaller  scale  than  those 
already  described,  is  rather  more  sharply  accentuated.  A  close 
relation,  as  has  been  said,  generally  exists  between  the  slope  of  this 
and  of  the  neighboring  land.  Cases,  however,  may  be  found  which 
might  appear,  at  first  sight,  exceptions  to  the  rule.  For  instance, 
off  the  coast  of  the  Landes  in  France  the  continuity  of  the  shallow 
sea  bed  is  broken,  near  Cape  Breton,  by  a  channel,  the  bottom  of 
which  lies  some  50  fathoms  below  the  submarine  plain  on  either 
side.  Again,  though  the  Baltic  is  a  shallow  sea,  all  parts  of  it  being 
less  than  a  hundred  fathoms  deep,  and  this  measurement  not  even 
being  approached  till  some  distance  south  of  the  island  of  Goth- 
land, a  deep  channel  exists  in  the  Cattegat,  which  passes  along  the 
Norwegian  coast  till  it  is  lost  in  the  Arctic  Ocean.  The  bed  of 
this  channel  lies  at  a  depth  of  about  400  fathoms.*  So  if  the  bed 
of  the  North  Sea,  with  the  adjacent  coast,  were  elevated  600  feet 
(Fig.  19),  and  replaced  by  a  great  plain  watered  by  the  rivers  of 
Britain  and  of  North  Central  Europe,  Norway  would  be  still  sepa- 
rated from  it  by  a  deep  salt  water  inlet  bounded  by  the  northwest 
coasts  of  Zealand  and  Southern  Sweden.  A  still  more  marked 
instance  of  these  irregularities  is  to  be  found  at  the  "Swatch  of  no 
ground,"  as  it  has  been  called  by  mariners,  in  the  Bay  of  Bengal. 
Here  the  delta  of  the  Ganges  is  fringed  with  low  islands  and 
swampy  banks  overgrown  with  mangroves.  For  fifteen  miles 
seaward  the  soundings  generally  do  not  exceed  16  fathoms. 
Beyond  the  contour  line  of  a  hundred  feet  the  sea  bed  descends 
gradually,  though  more  steeply.  But  from  the  deeper  part  of  the 
Indian  Ocean  a  long  narrow  inlet  extends  toward  the  mouth  of  the 
Ganges.  At  its  lower  end,  where  a  marked  indentation  in  the  sub- 
marine contour  line  is  first  perceptible,  soundings  of  900  fathoms 
are  obtained ;  these  decrease  rather  rapidly  to  600  fathoms,  and 
from  this  to  450  fathoms.  The  channel  has  now  become  very 

*The  deepest  soundings  are  in  the  Skager  Rack,  and  amount  to  437  fathoms. 


58  THE   STORY   OF  OUR  PLANET. 

strongly  defined,  and  is  continued,  shallowing  with  extreme  slow- 
ness, until  it  rises  up  more  rapidly  to  the  level  of  the  ordinary 
channel  of  the  Ganges.  But  even  at  the  above-named  distance 
from  the  coast  the  bed  of  the  Swatch  lies  1700  feet  below  the 
muddy  plateau  on  either  side.  Similar  interruptions,  compara- 
tively abrupt,  are  known  to  occur  in  other  parts  of  the  world,  and 
will  be  again  referred  to  in  a  later  part  of  this  volume.  It  will  be 
seen,  then,  that  they  are  generally  indicative  of  submerged  river 
valleys. 

If,  however,  these  cases,  apparently  exceptional,  be  put  aside,  the 
following  conclusions  result  from  a  study  of  the  contours  of  the 
beds  of  seas  and  oceans:  (i)  That,  as  already  said,  these  contours 
correspond  generally  with  those  of  the  neighboring  land,  but  that 
in  them  the  horizontal  scale  stands  in  a  different  relation  to  the 
vertical.  If  a  model  were  constructed  to  exhibit  the  contours  of 
the  land  surface  and  of  the  ocean  bed,  and  if  a  cast  were  taken  of 
this  in  some  flexible  material,  which  was  then  turned  so  as  to  make 
another  globe,  it  would  be  found  that  on  the  former  model  a  series 
of  ridges,  comparatively  narrow  and  steep,  formed  an  interrupted 
network,  in  the  wide  interstices  of  which  the  surface  shelved  down 
into  basins  of  variable  depth;  while  on  the  other  a  series  of  gently 
undulating  plateaus  was  parted  by  narrow  furrows,  the  beds  of 
which  were  broken  by  somewhat  deeper  pits,  corresponding,  of 
course,  with  the  mountain  peaks  of  our  globe.  (2)  That  the  floor 
of  the  ocean  does  not  descend  gradually  from  all  quarters  to  one 
lowest  point,  but  that  it  consists  of  a  number  of  basin-shaped  depres- 
sions. If  its  waters  were  to  be  gradually  dissipated  by  a  process 
of  evaporation,  so  that  island  were  united  to  island  and  continent  to 
continent,  the  single  continuous  ocean  would  be  broken  up  into 
two  or  three  huge  inland  seas,  which,  as  the  water  disappeared, 
would  be  further  subdivided  into  insulated  basins.  These,  how- 
ever, would  not  always  occur  at  the  greatest  distance  from  the 
present  coasts,  and  it  would  be  frequently  observed  that  in  the  case 
of  some  of  the  smaller  basins  land  elevation  and  ocean  depression 
stood  one  to  another  in  a  curious  relation,  something  like  that  of  a 
cast  and  its  mold.  To  this  reference  must  be  made  in  a  future 
chapter;  at  present  it  will  suffice  to  emphasize  the  fact  that  the 
earth's  surface,  speaking  figuratively,  is  dimpled  by  the  ocean 
basins  and  is  wrinkled  by  the  mountain  chains. 

The  great  mass  of  water  which  covers  so  large  a  part  of  the  globe 
is  in  constant  motion;  it  is  ruffled  by  the  winds;  it  is  swayed  by 


THE    WATER  REGION. 


59 


the  tides;  it  is  traversed  by  currents;  perhaps  only  in  its  most  pro- 
found abysses  is  it  actually  at  rest.  Of  these  disturbances  the 
waves,  which  are  the  direct  result  of  the  winds,  are  most  con. 
spicuous  to  man.  By  these  also  important  changes  are  brought 
about  in  the  contours  of  the  land,  a  subject  which  will  receive 
attention  in  a  future  chapter.  But  just  as  the  influence  of  the 
waves  is  rarely  felt  beyond  a  very  moderate  distance  above  the 
level  of  high  tide,  so  does  it  seldom  extend  to  any  great  depth 
below  low-water  mark,  very  commonly  not  even  so  far  as  twenty 
fathoms. 

The  winds  also  produce  considerable  effects  locally  on  the  actual 


FIG.  20. — THE  ATTRACTION  OF  THE  MOON  IN  PRODUCING  TIDES. 

M.    Direction  of  Moon;  a'6,  ab>,   Shell  of  Water. 

level  of  the  sea.  Many  years  since  it  was  observed  by  Smeaton 
that  a  steady  breeze,  when  blowing  along  a  canal  four  miles  in 
length,  caused  the  water  at  one  end  to  be  four  inches  higher  than 
at  the  other;  but  the  effects  on  larger  masses  are  on  a  far  greater 
scale.  In  the  estuary  of  the  River  Plate  the  level  of  the  water  may 
be  lowered,  when  a  southwesterly  gale  is  blowing,  by  from  twelve 
to  eighteen  feet  in  less  than  half  a  day ;  and  large  tracts  of  land 
are  laid  bare,  which,  when  the  wind  drops,  are  again  overflowed. 

The  tides  also — in  other  words,  the  joint  influence  of  the  sun  and 
moon — are  potent  factors  in  disturbing  the  ocean  waters.  Other 
planets  produce  similar  effects,  but  these  are  too  small  to  be  practi- 
cally appreciable.  If  the  earth  were  covered  with  water,  had  no 
moon,  and  presented  always  the  same  face  to  the  sun,  the  fluid 
would  take  the  shape  of  an  egg,*  one  end  pointing  toward  the  sun 
and  another  directly  away  from  it.  In  the  one  case  the  sun  tends 
to  draw  the  water  away  from  the  earth,  and  in  the  other  the  earth 

*  Strictly  speaking,  a  prolate  spheroid. 


60  THE   STORY  OF  OUR  PLANET. 

away  from  the  water,  so  that  the  same  result  is  produced  on  either 
side.*  If  the  earth  be  supposed  to  rotate,  as  it  actually  does,  about 
an  axis,  then  the  water  would  constantly  tend  to  assume  this  ovoid 
form,  so  that  its  surface  would  be  traversed  by  two  broad  waves, 
the  crests  of  which  would  be  180  degrees  apart.  The  moon,  if  it 
acted  alone,  would  produce  a  similar  effect,  so  when  both  are  acting 
the  result  at  one  time  represents  the  sum,  at  another  the  difference 
of  these  effects.  The  mass  of  the  sun  vastly  exceeds  that  of  the 
moon,  but  as  the  latter  is  so  much  nearer  than  the  former  to  the 
earth,  it  produces  the  greater  effect — the  tide  wave  due  to  the 
moon  being  about  five  feet  in  height,  and  that  due  to  the  sun  only 
about  two  feet.  If,  then,  the  straight  line  joining  the  centers  of 
the  sun  and  moon  pass  through  the  middle  of  the  earth,  their 
effects  are  combined,  whether  they  be  on  the  same  side  or  on  oppo- 
site sides  of  it,  and  the  result  is  a  "spring  tide,"  corresponding  with 
new  or  full  moon.  But  when  the  lines  joining  the  center  of  the 
earth  with  that  of  the  sun  and  with  that  of  the  moon  are  at  right 
angles,  then  the  solar  low  water,  as  it  might  be  called,  corresponds 
with  the  lunar  high  water,  and  the  actual  tide  with  the  difference 
between  them,  or  the  result  is  a  "neap  tide." 

As,  however,  the  ocean  is  interrupted  by  continents  and  land 
masses,  the  phenomena  of  the  tides  are  of  a  much  more  complicated 
character  than  in  the  ideal  case  which  has  been  described.  Strictly 
speaking,  a  tidal  wave  is  generated  in  every  sheet  of  water,  but  the 
disturbing  influence  acts  for  too  short  a  time  on  even  the  largest 
lake  to  produce  any  perceptible  effect.  Even  in  the  Mediterranean 
the  difference  between  high  and  low  water  is  but  slight — in  the 
more  open  parts  not  more  than  from  one  to  two  feet.  The  tidal 
waves  take  their  origin  in  the  greater  ocean  basins,  and  roll  onward 
toward  the  coasts.  As  the  depth  of  the  water  diminishes  the  pace 
of  the  wave  decreases,  but  its  effect  becomes  more  marked ;  with  a 
shallowing  sea  bed  and  a  narrowing  channel  the  advancing  wave, 
as  it  were,  becomes  piled  up,  and  the  difference  between  high  and 
low  water  increases.  For  instance,  on  the  coasts  of  South  Wales 
and  Devonshire  it  amounts  to  about  27  feet  at  the  mouth  of  the 
Bristol  Channel,  and  it  gradually  increases  as  the  shores  converge, 

*  If  the  mass  of  the  sun  be  represented  by  M,  the  distance  of  its  center  from  that  of  the 
earth  by  R,  and  the  radius  of  the  latter  by  r,  then  the  difference  between  the  attraction  of 
the  sun  on  the  earth  as  a  whole,  and  its  attraction  on  a  particle  placed  on  the  surface  of 

the  latter,  in  the  line  joining  the  centers,  is  represented  approximately  by    -  — — 


THE    WATER  REGION.  61 

till  at  last  it  is  as  much  as  42  feet  in  the  estuary  of  the  Avon  and 
about  50  feet  in  that  of  the  Wye.* 

Occasionally,  however,  a  tidal  chart  exhibits  results  which  seem 
to  be  anomalous.  Near  the  mouth  of  the  Wash  the  difference 
between  high  and  low  water  is  20  feet ;  thence  it  diminishes  east- 
ward along  the  Norfolk  coast,  though  the  bed  of  the  North  Sea  is 
becoming  both  shallower  and  narrower,  until  at  Lowestoft,  in 
Suffolk,  it  amounts  only  to  6  feet.  The  anomaly,  however,  is 
apparent,  not  real.  The  tidal  wave  is  generated,  not  in  British 
seas,  but  in  the  open  Atlantic.  As  it  approaches  these  islands,  it 
is  parted  by  them  as  is  a  stream  by  the  pier  of  a  bridge :  one 
branch  passes  up  the  English  Channel,  and  even  makes  its  way 
through  the  Straits  of  Dover,  the  other  flows  into  the  North  Sea, 
round  the  shores  of  Scotland.  Each  of  these  branches  affects  the 
water  between  the  East  Anglian  and  the  Dutch  coasts,  but  paths 
of  different  length  have  been  necessarily  traversed  in  order  to  reach 
this  region,  and  so  the  waves  arrive  in  a  different  phase  of  move- 
ment. Opposite  to  Lowestoft  this  differs  by  six  hours,  or,  in  other 
words,  when  it  is  high  tide  for  the  one  wave  it  is  low  tide  for  the 
other.  They  do  not,  however,  neutralize  one  another,  because  one 
wave  has  been  diminished  in  power  by  its  passage  through  the 
Straits  of  Dover;  still  it  is  sufficiently  potent  to  reduce  the  differ- 
ence between  high  and  low  water  by  at  least  four  yards.f 

The  tides,  however,  like  the  large  rivers  which  flow  into  the  sea, 
only  produce  movements  of  transference  in  its  waters  compara- 
tively near  to  the  coast.  Other  movements  exist,  the  effects  of 
which,  though  at  first  sight  inconspicuous,  are  in  reality,  as  will  be 
subsequently  explained,  of  the  utmost  importance.  These  may  be 
distinguished  as  the  ocean  currents  and  the  oceanic  circulation. 
The  former  may  be  compared  to  the  draughts  which  are  so  often 
an  annoyance  in  a  room,  the  latter  to  the  slow  movement  of  the  air 
when  the  ventilation  is  good.  As  in  this  case,  so  also  in  the  ocean, 
the  former  attract  the  greater  attention.  This,  however,  is?  not  sur- 
prising, since  the  currents  directly  affect  the  surface  of  the  ocean. 

*  Seventy-two  feet  is  given  as  a  rare,  but  possible,  difference  between  high  and  low 
water.  See  Lyell,  "  Principles  of  Geology,"  ch.  xx. 

f  In  some  cases,  as  in  the  channel  formed  by  a  large  island,  the  tide,  after  falling  for  a 
little  time,  again  flows  back.  Thus  at  Southampton  the  water,  after  ebbing  for  about  half 
an  hour,  again  returns  before  its  final  retreat.  The  reflux  is  produced  by  the  portion  of 
the  tidal  wave  which  has  made  its  way  into  the  eastern  part  of  the  Solent,  after  flowing 
from  the  westward,  round  the  south  side  of  the  Isle  of  Wight. 


THE    WATER   REGION.  63 

They  are  restricted  to  the  upper  layer  of  its  waters,  and  their 
influence  probably  seldom  extends  to  a  depth  of  more  than  a  very 
few  hundred  feet.  Like  all  other  currents,  they  follow  paths  fairly 
well  defined,  and  have  been  termed,  not  inaptly,  the  rivers  of  the 
ocean.  But  the  oceanic  circulation  disturbs  enormous  masses  of 
water — its  effects  in  some  cases  extend  down  to  the  greatest 
depths ;  probably  only  the  most  profound  abysses  of  the  insulated 
basins  escape  from  its  influence  and  contain  water  which  is  abso- 
lutely stagnant.  But  this  circulation  has  to  be  inferred  rather  than 
detected  by  direct  observation.  It  is  revealed,  not  by  the  ordinary 
experimental  tests,  but  by  a  comparative  study  of  the  records  of 
deep-sea  temperature.  This  indicates  that  the  deeper  ocean  waters 
cannot  be  in  equilibrium,  but  those  of  high  and  low  latitudes  must 
be  in  constant  process  of  exchange. 

Currents  exist  in  all  seas,  and  traverse  each  of  the  greater  ocean 
basins.  In  the  latter  case  they  may  be  traced  for  some  hundreds 
of  miles;  they  transfer  water  from  equatorial  to  polar,  and  from 
polar  to  equatorial  regions,  forming,  as  it  were,  a  hot  and  cold 
water  system  on  the  surface  of  the  globe,  and  so  becoming  factors 
of  much  importance,  as  will  be  seen  presently,  in  determining  the 
climate  of  particular  localities.  The  map  (Fig.  21)  indicates  their 
general  distribution  and  relation;  it  maybe  sufficient  to  restrict 
any  detailed  description  to  the  one  which  bears  the  name  of  the 
Gulf  Stream,  since  it  is  the  best  known  and  is  of  most  importance 
to  the  inhabitants  of  these  islands.  This,  as  is  commonly  said,  has 
its  origin  in  the  Gulf  of  Mexico— that  may  be  regarded  as  the 
boiler  in  which  a  great  mass  of  water  is  raised  to  a  temperature 
some  degrees  higher  than  the  average  of  neighboring  seas.  But  a 
boiler,  if  its  outflow  pipe  were  left  running,  would  soon  be  emptied,  if 
not  provided  with  a  feeder.  So  the  Gulf  of  Mexico  is  supplied  from 
the  Caribbean  Sea,  and  that  receives  a  current  which  sweeps  along 
the  South  American  coast  northward  from  Cape  S.  Roque,  and  so 
on.  But  to  return  to  the  Gulf  Stream.  It  passes  into  the  Atlantic, 
as  through  a  gigantic  floodgate,  between  the  peninsula  of  Florida  on 
the  one  side  and  the  island  of  Cuba  and  the  Bahamas  on  the 
other — a  mighty  stream,  about  37  miles  in  breadth,  the  depth  of 
which  is  estimated  at  about  200  fathoms,  and  the  velocity  at  about 
3^2  miles  an  hour  on  the  average,  though  it  sometimes  attains  to 
nearly  5  miles.  Various  statements  have  been  made  as  to  the 
quantity  of  water  discharged  by  this  huge  ocean  river.  On  a 
moderate  estimate  it  is  two  thousand  times  that  of  the  Mississippi, 


64  THE   STORY  OF  OUR   PLANET. 

but  by  some  authors  it  is  considered  to  be  very  much  more. 
Broadening  as  it  flows,*  the  Gulf  Stream,  toward  latitude  40°  N., 
gradually  divides  itself  into  two  branches.  Of  these  the  eastern 
one  sweeps  round  by  the  Azores,  and  is  deflected  first  in  a  southern, 
then  almost  in  a  western  direction,  until  it  is  lost  at  last  in  the  still 
waters  of  the  Sargasso  Sea.  The  other  branch  maintains  a  north- 
easterly course,  gradually  broadening  out  and  becoming  less  easily 
recognized  as  it  approaches  the  western  shores  of  Europe.  Geogra- 
phers are  at  issue  as  to  how  far  in  this  direction  it  can  be  traced  as 
the  Gu/f  Stream.  Some  hold  that  it  cannot  be  identified  after  it 
has  reached  approximately  the  latitude  of  Lisbon,  while  others 
maintain  without  hesitation  that  it  washes  the  western  coasts  of 
Britain,  and  even  of  Norway,  and  produces  effects,  direct  or  indi- 
rect, so  far  north  as  Spitzbergen. 

A  current  in  any  direction,  unless  the  water  thus  transferred  be 
removed  in  some  other  way,  must  imply  a  return  current  in  the 
opposite  one,  and  the  exceptions  to  this  rule  are  not  likely  to  be 
numerous.  So  a  current  parallel  with  the  Gulf  Stream  flows  south- 
ward from  the  Arctic  regions  (Fig.  22).  Currents  of  water,  if  flow- 
ing in  the  direction  of  lines  of  longitude,  of  course  are  deflected  by 
the  rotation  of  the  earth  in  the  same  way  as  winds,  and  they  obey 
the  same  law.  Thus  the  Gulf  Stream  keeps  edging  away  toward 
the  east,  and  the  return  current,  which  is  formed  by  a  combination 
of  the  "Arctic  current"  down  the  east  shores  of  Greenland  with  the 
one  flowing  between  that  country  and  Labrador,  skirts  the  Ameri- 
can coast  until  it  disappears  beneath  the  waters  of  the  Gulf  Stream. 

The  Gulf  Stream  and  other  ocean  currents  are  conspicuous  phe- 
nomena. Their  existence  is  indicated  by  the  transport  of  floating 
bodies,  as  when  the  West  Indian  bean  is  washed  up  even  on  the 
shores  of  Iceland,f  or  by  the  marked  difference  in  the  temperature 
and  by  other  characteristics  of  the  surface  water.  That  of  the  Gulf 
Stream,  for  instance,  has  a  blue  tint,  that  of  the  returning  American 
current  a  greenish  one,  and  the  two  masses  are  sometimes  divided 
almost  as  sharply  as  the  Rhone  and  the  Arve  at  their  confluence 
below  Geneva.  But  the  existence  of  the  oceanic  circulation  is  far 
less  easily  detected.  This  was  only  established  when  the  tempera- 

*  Between  the  Bermudas  and  New  York  (early  in  May,  1873)  the  Gulf  Stream  was 
estimated  as  about  60  miles  wide  and  100  fathoms  deep,  running  at  the  rate  of  three  knots 
an  hour. — "Voyage  of  the  Challenger  "  (The  Atlantic,  ch.  v.). 

f  Entada  gigalobium^  from  the  Antilles,  has  been  found  even  on  the  coast  of  Spitz- 
bergen.—Reclus,  "  The  Ocean,"  ch.  viii. 


THE    WATER   REGION. 


ture  of  the  ocean  down  to  great  depths  had  been  ascertained  by  a 
series  of  observations  which  were  rendered  practicable  by  improved 
methods  of  sounding.  One  instance  of  this  circulation — that  which 
has  been  discovered  in  the  Atlantic — may  be  sufficient.  On  either 


FIG.  22. — DIRECTION  OF  CURRENTS  TO  AND  FROM  THE  ARCTIC  OCEAN. 

side  of  the  equator,  for  full  35°  of  latitude,  the  bed  of  the  ocean, 
excepting  comparatively  near  the  shore  and  in  one  or  two  deeper 
basins,  varies  in  depth,  roughly,  from  about  1500  to  2500  fathoms, 
and  it  shallows  slightly,  but  still  definitely,  in  a  southerly  direction. 
In  the  northern  part  of  this  area  the  bottom  temperature  is  about 
36°  F.,  but  it  falls,  of  course,  toward  the  polar  edge  of  the  basin. 
But  after  a  time  the  temperature  decreases  still  more  perceptibly  in 
a  southward  direction ;  about  latitude  20°  N.  it  reaches  34°  F.,  and 
under  the  equator  is  even  as  low  as  32.4°  F.,  or  only  slightly  above 
the  freezing  point  of  fresh  water.  If  submarine  isotherms  are 
plotted  down  on  a  section  of  the  Atlantic  from  latitude  40°  N.  to 
40°  S.,  the  line  of  35°  F.,  as  it  comes  from  the  latter  sidet  is  seen  to 


66  THE   STORY  OF  OUR  PLANET. 

slope  downward  in  the  North  Atlantic  till  it  strikes  the  bottom 
about  latitude  20°  N.,  and  then  disappears  for  a  considerable  time. 
Similar  bends  are  shown  by  the  other  lines  of  equal  temperature  in 
the  deeper  parts  of  the  ocean.  It  is  therefore  clear  that  as  the  icy 
sea  which  surrounds  the  southern  circumpolar  land  is  so  much 
greater  in  volume  than  the  Arctic  Ocean,  with  its  limited  area, 
narrow  straits,  and  ramifying  channels,  the  zone  of  highest  bottom 
temperature  in  the  Atlantic  lies,  not,  as  it  might  be  expected, 
immediately  under  the  equator,  but  much  nearer  to  the  Tropic  of 
Cancer;  or,  in  other  words,  that  the  Antarctic  water,  creeping  down 
along  the  ocean  floor,  overshoots  the  equator. 

The  principal  cause  of  ocean  currents  is  at  present  a  matter  of 
dispute.  The  oceanic  circulation,  it  can  hardly  be  doubted,  is 
mainly  due  to  differences  of  temperature;  and  by  some  authorities 
the  ocean  currents  are  attributed  to  the  same  cause.  That  the 
equilibrium  of  their  waters  is  disturbed  by  heat  in  more  than  one 
way  can  hardly  be  doubted.  Under  the  equator  the  mean  annual 
surface  temperature  is  often  as  high  as  80°  F. ;  in  latitude  55°  on 
either  side  it  may  fall  below  40°  F.  By  this  a  circulation  is  cer- 
tainly caused;  a  current  also  may  be  produced  in  some  cases, 
especially  if  the  shelving  coast  of  a  continent  tends  to  "bank  up"  the 
colder  water.  Again,  the  level  of  the  sea  in  equatorial  regions  is 
lowered  by  evaporation,  a  mass  of  water  being  annually  removed 
from  the  whole  surface  which  can  hardly  be  less  than  twelve  feet  in 
thickness.  Much  of  this,  no  doubt,  is  returned  either  almost 
immediately  as  rain  or  before  long  by  the  rivers  draining  tropical 
lands;  still  this  loss  must  considerably  lower  the  ocean  surface,  and 
equilibrium  must  be  restored  by  an  influx  from  regions  where  the 
evaporation  is  comparatively  slight.  That  the  sun  is  a  pumping 
engine  of  mighty  force  can  be  proved  by  a  single  instance.  The 
area  of  the  Dead  Sea  is  about  330  square  miles;  from  it,  as  is  well 
known,  no  river  issues,  so  that  the  inflowing  water  must  either  be 
absorbed  by  the  earth,  which  is  not  likely  to  happen  to  any  great 
extent,  or  be  removed  by  evaporation.  The  Jordan,  just  before 
entering  the  Dead  Sea,  is  80  yards  wide  and  7  feet  deep,  and  flows 
at  the  rate  of  3  knots  an  hour.  Hence  the  volume  of  water  dis- 
charged by  the  river  into  the  sea  should  suffice  in  the  course  of  a 
year  to  form  a  layer  over  the  whole  area  not  less  than  10  feet  thick. 
But  as  no  permanent  rise  takes  place  in  the  level  of  the  waters,  this 
quantity  at  least  (for  no  notice  has  been  taken  of  the  rainfall  or  of 
smaller  tributary  streams)  must  be  pumped  up  by  the  sun  from  the 


THE    WATER  REGION.  67 

surface  of  the  Dead  Sea.  But  the  same  process  must  affect  seas 
and  the  ocean  generally  in  the  warmer  regions  of  the  globe.  For 
instance,  hardly  any  water  is  contributed  to  the  Red  Sea  by  rain  or 
by  rivers,  while  the  amount  which  is  removed  by  evaporation  can- 
not be  less  than  eight  feet  annually  from  the  whole  surface,  and 
may  well  be  rather  more.  The  loss,  then,  must  be  supplied  by  an 
inflow  from  the  Indian  Ocean  through  the  Strait  of  Bab-el-Mandeb, 
and  this  current  is  known  to  exist. 

Moreover,  changes  of  temperature  affect  the  specific  gravity  of 
water.  This  operates  in  a  direct  and  in  an  indirect  way.  Water 
expands  when  heated  and  contracts  when  cooled,  so  that  a  cubic 
foot  of  it  obtained  at  the  equator  weighs  less  than  the  same  quan- 
tity taken  up  at  the  Arctic  Circle.  What  must  happen  when  the 
two  are  in  communication  can  be  demonstrated  by  a  very  simple 
experiment.*  Take  a  small  glass  tank,  such  as  a  common 
aquarium,  and  fill  it  with  water.  On  the  top  of  a  piece  of  black 
rock,  a  few  cubic  inches  in  volume,  sprinkle  some  cochineal,  and 
put  this  close  to  one  end  of  the  tank,  introducing  it  into  the  water 
so  carefully  and  gently  as  not  to  disturb  the  coloring  matter. 
Then  fix  a  good  convex  lens  in  such  a  position  that  the  rays  of  the 
sun  are  brought  to  a  focus  upon  the  piece  of  rock ;  at  the  same  time 
place  on  the  water,  at  the  opposite  end,  a  lump  of  ice,  and  upon 
this  pour  a  small  quantity  of  milk.  As  the  rock  is  heated  the  sur- 
rounding water,  which  is  becoming  stained  by  the  cochineal,  is 
warmed ;  it  expands,  and  a  red  cloud  mounts  upward.  But  at  the 
other  end  of  the  tank  the  water,  which  is  rendered  slightly  turbid 
by  the  milk,  is  chilled  by  contact  with  the  floating  ice,  and  so  a 
whitish  cloud  sinks  downward.  Presently  the  former  begins  to 
drift  along  the  surface  toward  the  ice,  the  latter  along  the  bottom 
toward  the  heated  rock,  and  thus  a  system  of  oceanic  circulation  is 
established.  But  it  is  difficult  to  understand — even  if  every  allow- 
ance be  made  for  the  effects  of  continental  barriers  and  irregulari- 
ties in  the  ocean  bed — how  these  slow,  creeping  movements  of  vast 
masses  of  water  can  be  converted  into  the  more  limited  and  super- 
ficial, but  more  active,  phenomena  of  currents.  In  Nature  a  cause 
may  be  a  true  one,  yet  not  the  principal  cause.  Rivers  by  their 
influx,  the  tides  as  they  ebb  and  flow,  solar  evaporation  and 
changes  of  temperature,  may,  and  in  some  cases  certainly  do,  pro- 

*  It  was  devised  and  described  by  the  late  Mr.  J.  F.  Campbell  in  "  Frost  and  Fire," 
vol.  i  p.  68,  a  book  as  entertaining  as  it  is  suggestive. 


68  THE    STORY  OF  OUR  PLANET. 

duce  effects;  still  all  these  seem  inadequate  to  explain  such  a  cur- 
rent as  the  Gulf  Stream.  So  another  solution  has  been  sought,  and 
many,  perhaps  the  majority,  of  those  who  have  studied  the  ques- 
tion regard  the  ocean  currents  as  produced  by  the  wind.  But  with 
this  general  statement  complete  agreement  ceases.  For  instance, 
in  the  case  of  the  Gulf  Stream,  some  attribute  it  to  the  action  of 
the  trade  winds,  which  either  force  the  water  into  the  Gulf  of 
Mexico,  where  it  is  piled  up,  so  as  to  flow  by  gravitation  through 
the  other  outlet,  or  impel  it  forward,  as  the  water  on  the  surface  of 
a  pond  is  driven  before  a  puff  of  wind.  But  neither  of  these  expla- 
nations seems  satisfactory.  Each,  like  those  previously  considered, 
may  be  a  partial  statement  of  the  truth,  but  both  appear  inade- 
quate to  produce  effects  so  strongly  marked.  So  a  more  compre- 
hensive explanation  has  been  proposed.  In  this  it  is  maintained 
that  the  currents,  whether  in  the  ocean  or  in  the  air,  cannot  be 
regarded  as  isolated  phenomena.  They  form  systems,  the  several 
parts  of  which  are  more  or  less  connected  and  linked  together. 
Thus  the  ocean  currents,  as  a  whole,  are  produced  by  the  aerial 
currents,  also  acting  as  a  whole.*  This  supposition  is  confirmed  by 
a  comparison  of  charts  representing  the  paths  of  each.  The  modi- 
fications introduced  by  the  intervention  of  land  masses  are  doubt- 
less more  important  in  the  case  of  the  ocean  currents;  at  the  same 
time  a  relation  exists  between  these  and  the  more  permanent  atmos- 
pheric currents  sufficient  to  render  it  highly  probable  that  the  one 
stands  to  the  other  in  the  position  of  effect  and  cause. 

We  have  said  that  rain  and  rivers  feed  the  ocean.  But  it  is  at 
once  their  grave  and  their  birthplace;  for  without  the  ocean  there 
would  be  no  rain,  and  without  rain  there  would  be  no  rivers.  It  is 
needless  to  add  that  without  the  sun's  heat  there  would  be  neither 
rain  nor  rivers  nor  ocean ;  for  there  would  be  no  atmospheric 
circulation,  no  evaporation,  nothing  to  precipitate,  for  water  would 
only  exist  as  a  solid  rock,  since  the  temperature  of  the  earth  would 
be  that  of  outer  space. f  The  cause  and  distribution  of  rain  have 
been  already  sketched  in  the  chapter  dealing  with  the  atmosphere, 
to  which  it  seems  more  naturally  to  belong.  The  effect  of  rain, 
whether  acting  directly  or  when  collected  in  rivers,  belongs  to  a 
later  part  of  the  subject,  but  the  history  of  water  in  the  form  of 
snow  and  ice  requires  a  brief  notice  before  this  region  is  finally 
quitted. 

*Croll,  "Climate  and  Time,"  ch.  xiii. 

f  Estimated  as  —239°  F.,  or  271°  below  the  freezing-point  of  water. 


THE    WATER  REGION. 


69 


Water,  under  atmospheric  pressure,  becomes  a  crystalline  solid 
at  a  temperature  of  32°  F.  In  the  fairy  flowers  built  up  during  a 
hard  frost  from  the  vapor  in  a  room  upon  the  cold  surface  of  the 
window  glass,  in  the  tiny  stars,  with  each  of  their  six  rays  like  a 
frond  of  frozen  fern,  showered  down  from  the  clouds  on  a  calm 
winter  day,  the  crystals  exhibit  their  true  form.*  But  in  ordinary 
ice  they  are  massed  more  or  less  irregularly  together;  in  ordinary 


FIG.  23. — SNOW  CRYSTALS. 

snow  they  are  broken  by  the  breeze,  and  are  gathered  as  they  drift 
through  the  air  into  irregular  flakes.  The  same  process  of  accumu- 
lation—"the  little  making  a  mickle" — continues  as  the  ground  is 
covered  by  the  falling  flakes,  and  layer  piled  on  layer  forms  beds  of 
snow.  These,  when  heaped  up  in  sufficient  masses  and  under 
favorable  circumstances,  are  the  sources  of  glaciers.  In  temperate 
regions  where  the  land  lies  comparatively  low  the  snowfall  of 
winter  disappears  before  the  warm  sun  and  winds  of  summer;  but 
in  more  arctic  lands,  or  where  mountain  ranges  rise  high  enough 
above  the  sea  to  give  a  suitable  climate,  the  contrary  result  is  pro- 
duced. The  snow  accumulates;  the  results  are  snowfields,  glaciers, 
and  ice-caps. 

In  a  mountain  region  like  the  Alps  the  process  of  the  formation  of 
a  glacier  can  be  seen  in  its  several  stages.  At  a  certain  height  above 
the  sea  the  mean  annual  temperature  sinks  to  32°  F.  Permanent 


*  Ice  belongs  to  the  hexagonal  system  of  mineralogists,  and  is  modeled  on  a  six-sided 
prism. 


70  THE   STORY  OF  OUR  PLANET. 

beds  of  snow  are  found  shortly  above  this  line  ;  in  the  Alps  they  begin 
at  about  eight  thousand  feet ;  the  exact  position  being  dependent 
upon  a  number  of  circumstances,  such  as  the  nature  of  the  rock, 
the  configuration  and  aspect  of  the  ground,  and  the  like.*  These 
beds,  however,  do  not  increase  beyond  a  certain  amount,  for  after 
that  has  been  reached  the  warm  weather  expenditure  exhausts  the 
cold  weather  supply,  accumulation  in  the  earlier  stages  being  the 
result  of  favorable  circumstances  dependent  on  the  locality.  As  a 
rough  illustration,  they  may  be  likened  to  a  man  who  has  suc- 
ceeded in  saving  a  small  capital  early  in  life,  but  afterward  is 
obliged  to  live  up  to  his  income.  They  do  not  form  true  glaciers, 
but  remain  as  snowbeds.  One  change,  however,  takes  place  which 
makes  them  differ  from  ordinary  masses  of  fresh-fallen  snow.  As 
their  upper  surface  is  melted  by  the  warmer  air,  much  of  the  water 
so  produced  trickles  down  into  the  underlying  mass.  But  on  this 
journey  through  the  frozen  particles  it  is  robbed  of  its  own  tiny 
store  of  heat,  which,  however,  is  insufficient  to  produce  in  them  any 
material  change,  being  of  no  more  use  than  a  hungry  man's  last 
crust  of  bread  among  a  famished  multitude ;  so  the  water  goes 
back  again  into  ice,  and  the  snow  by  this  process  is  gradually 
cemented  together  into  a  fairly  solid  mass.  The  weight  also  of  the 
upper  layers  helps  in  solidifying  the  lower,  for,  as  has  been  demon- 
strated by  experiment,  a  heap  of  loose  snow  can  be  converted  by 
the  use  of  an  hydraulic  press  into  a  cake  of  solid  ice ;  f  but  this 
action  becomes  important  only  at  a  later  stage,  when  the  thickness 
of  the  accumulated  mass  is  materially  increased.  Both  causes 
operate  in  converting  snow  into  ice;  but  at  first  the  one,  afterward 
the  other,  plays  the  more  important  part. 

At  an  elevation  of  about  a  thousand  feet  higher  on  the  slopes, 
supposing  other  conditions  favorable,  the  snowbed,  particularly 
if  lodged  in  a  depression,  such  as  the  head  of  a  shallow  valley,  is 
found  to  be  slightly  prolonged  in  a  downward  direction,  and  its 
lower  part  presents  a  nearer  resemblance  to  ordinary  ice.  This  is 
the  first  stage  in  the  formation  of  a  glacier.  At  a  somewhat  higher 
level,  particularly  when  the  head  of  the  valley  is  encircled  by  moun- 
tain peaks,  a  glacier  is  completely  developed.  The  surrounding 

*  In  addition  to  the  above-named  causes  of  variation,  the  snow  line,  which  is  about  seven 
hundred  feet  higher  than  where  the  mean  annual  temperature  is  32°  F.,  lies  lower,  owing 
to  the  geographical  position,  by  at  least  the  same  amount,  in  the  northern  part  of  the  Alps 
than  it  does  in  the  southern. 

f  Tyndall,  "  Heat  as  a  Mode  of  Motion,"  ch.  vi. 


THE    WATER  REGION.  71 

crags  remain  bare,  though  snow  has  lodged  on  their  ledges  and 
gathered  in  their  gullies;  but  it  has  cast  a  thick  mantle  on  every 
slope,  and  the  icy  covering  streams  down  like  a  flowing  robe  into 
the  recess  in  which  the  valley  has  its  origin.  Here  also,  just  as 
already  described,  the  snow  has  gathered,  and  is  often  augmented 
by  avalanches .  from  above,  as  the  fresh-fallen  layer  slips  off  from 
the  hard  crust  of  the  old  snow.  On  the  peaks,  and  in  the  combe 
beneath,  the  accumulated  material  is  in  the  intermediate  condition 
between  snow  and  ice.  The  mass  is  sufficiently  solid  to  rupture 
under  considerable  strain,  yet  it  often  retains  indications  of  the 
process  by  which  it  has  been  formed,  bed  above  bed  being  exposed 
in  fissures,  as  in  any  cliff  of  stratified  rocks.  It  is  imperfectly 
transparent;  is  white  in  color,  owing  to  the  numerous  tiny  bubbles 
of  imprisoned  air;  and  the  light  which  struggles  through  it  and 
faintly  illuminates  the  deeper  chasms  is  green  rather  than  blue.  The 
mass  which  has  thus  accumulated  moves  down  the  shelving  bed  of 
the  valley,  creeping  on  like  a  stream  of  hardening  mud  or  tar,  or 
lava;  and  so  a  glacier  is  formed.  The  head  of  a  mountain  valley  is 
almost  always  more  or  less  bowl-shaped,  and  the  sides  a  little  lower 
down  contract,  so  as  to  form  a  passage  comparatively  narrow. 
Through  this  the  descending  ice  is  forced  by  the  pressure  of  the 
mass  above.  It  suffers  as  the  individuals  of  a  crowd  in  a  struggle 
to  escape  from  a  hall  down  a  narrow  passage.  The  molecules  are 
squeezed  close  together;  the  interstitial  air  is  extruded  ;  the  porous 
granulated  mass — half  snow,  half  ice* — is  changed  into  solid  ice. 
The  stratified  structure  of  the  mass  in  the  upper  basin  is  completely 
lost,  and  a  new  structure,  as  a  rule,  appears.  As  to  the  cause  of 
this,  much  controversy  formerly  existed ;  but  it  is  now  generally 
considered  to  be  the  result  of  pressure.  This — the  banded  struc- 
ture, as  it  is  usually  called — consists  of  alternating  layers  of  white 
and  of  blue  ice,  the  former  being  full  of  tiny  air  bubbles.  These 
layers  vary  in  thickness,  ranging  roughly  from  half  an  inch  to  an 
inch  and  a  half.  The  structure  is  easily  seen  where  chasms  permit 
a  view  into  the  mass  of  the  glacier.  On  the  surface  they  are  dis- 
closed by  their  unequal  weathering,  the  more  porous  bands  yield- 
ing more  readily  to  the  disintegrating  effects  of  the  atmosphere. 
In  a  short  time  also  the  fine  dust,  blown  by  storms  from  the  crags 
on  either  side  of  the  valley,  lodges  in  the  furrows,  and  makes  the 
structure  yet  more  conspicuous,  so  that  it  can  be  seen  from  a  con- 

*  Called  w/z'/  in  the  French  districts  of  the  Alps,  and  firn  in  the  German. 


72  THE   STORY  Of  OUR  PLANET. 

siderable  distance.     Not  seldom    it    is    faithfully  recorded    in    the 
photographs  of  glaciers. 

As  the  glacier  descends  into  warmer  regions  it  melts  away. 
Some  of  the  effects  of  this  change  will  be  more  appropriately 
described  in  a  later  chapter;  at  present  it  may  suffice  to  say  that 
the  water  thus  produced  runs  for  a  time  in  streamlets  on  the  ice, 
is  engulfed  in  fissures,  carves  out  for  itself  subglacial  channels,  and 
ultimately  emerges  as  a  torrent  at  the  end  of  the  glacier.  Here, 


FIG.  24. — TERMINAL  ICE-CAVE  AND  BIRTHPLACE  OF  A  RIVER. 

generally,  a  shallow  cavern  is  formed  in  the  ice — a  blue  grotto, 
often  of  singular  beauty.  Its  charms,  however,  like  those  of  a 
siren,  are  best  contemplated  from  a  respectful  distance,  for  now  and 
then  large  masses  of  ice  come  crashing  down  from  the  roof,  break- 
ing away  without  the  slightest  warning.*  The  lower  limit  of  a 
glacier  depends  primarily  upon  temperature,  secondarily  upon  a 
variety  of  local  circumstances,  a  discussion  of  which  would  demand 
too  much  space.  In  the  Alps  the  larger  glaciers  never  descend  much 
below  four  thousand  feet  above  sea  level,  and  seldom  quite  reach  this 
limit.  But  the  limit,  and  of  course  the  volume,  of  the  glaciers  in 
any  region  is  by  no  means  constant.  Taking  the  Alps  as  an 
example,  changes  not  unimportant  have  occurred  within  the  last 
three  centuries,  even  within  the  memory  of  many  now  living.  The 
facts  at  present  on  record  are  insufficient  to  determine  accurately 

*I  was  sketching  one  clay  the  ice  cave  at  the  end  of  the  Rhone  glacier  (of  course,  at  a 
perfectly  safe  distance),  when  a  mass  of  ice,  more  than  enough  to  load  a  cart,  dropped  sud- 
denly from  the  roof. 


THE  WATER  REGION.  73 

the  period  of  increase  and  decrease — probably  it  is  not  capable  of  a 
simple  expression — but  apparently  it  is  something  like  half  a  cen- 
tury. For  nearly  thirty  years  the  tide  of  the  Alpine  ice  has  been 
slowly  ebbing;  it  seems  now  to  be  turning  again.  We  who  knew 
the  glaciers  at  the  beginning  of  that  period— about  the  year  1860 — 
can  remember  how  marked  a  change  took  place  during  the  follow- 
ing decade.  Of  this  it  may  suffice  to  quote  a  single  instance.  The 
Unter-Grindelwald  glacier  in  1858  descended  to  the  bed  of  the 
valley  between  it  and  the  village,  and  one  could  step  without  diffi- 
culty from  the  level  part,  above  the  last  icefall,  onto  the  rocks  near 
the  Baregg  Chalet.  In  1870  slopes  and  crags  of  ice-worn  rock — 
some  200  yards  in  vertical  height — intervened  between  the  bed  of 
the  valley  and  the  ravine  in  which  the  glacier  hid  its  diminished 
head ;  while  from  the  neighborhood  of  the  chalet  one  looked  upon 
the  ice  down  cliffs,  which  indicated  that  its  thickness  in  this  part 
had  been  diminished  by  some  60  or  70  feet. 

The  rate  at  which  an  ice  stream  moves  varies  in  different  parts  of 
the  same  glacier  and  in  different  regions.  It  obeys  always  the  same 
rule  as  a  river,  its  motion  being  more  rapid  in  the  middle  than  at 
the  sides,  and  in  the  upper  than  in  the  lower  part.  Its  pace  is 
quicker  in  the  summer  than  in  the  winter.  The  greater  Alpine 
glaciers  in  the  course  of  a  year  move  through  about  as  many  feet 
as  there  are  days.*  But  the  huge  glaciers  of  Greenland  appear  to 
travel  at  a  less  deliberate  pace.  To  them  the  latest  published 
observations  assign  velocities  which  vary,  according  to  circum- 
stances, from  about  20  to  40  feet  a  day,  the  great  Jakobshaven 
glacier  even  attaining  to  50  feet.  As  a  rough  average,  they  may  be 
said  to  move  about  thirty-five  times  as  fast  as  the  glaciers  of  the 
Alps.f 

The  precise  cause  of  the  motion  in  a  glacier  has  long  been  a  sub- 
ject of  controversy  among  physicists.  A  full  discussion  of  its 
details  would  extend  this  chapter  to  an  inordinate  length,  so  that 
a  very  brief  summary  must  suffice.  The  various  theories  may  be 
ranged  in  two  groups,  the  one  regarding  gravitation,  the  other  heat, 


*The  following  are  more  precise  statements  (quoted  by  Prestwich,  "Geology,"  part  ii. 
ch.  xxxiii.) : 

Glacier  du  Bois  (mean  of  5  years)  364  feet  per  annum. 
Rhone  Glacier  (     "  7     "    )  366  " 

Aar  Glacier        (     "         14     "    )  338  " 

fSee  Prestwich,  "  Geology,"  part  ii.  ch.  xxxiii.,  for  numerous  details  and  a  discussion 
of  the  consequences  to  which  these  facts  point. 


74  THE  STORY  OF  OUR  PLANET. 

as  the  ultimate  motive  cause.  De  Saussure,  who  was  the  first  to 
make  any  scientific  investigation  of  glaciers,  contented  himself  with 
remarking  that  they  slid  down  the  rocky  beds  of  valleys  as  a  result 
of  gravitation.  It  was,  however,  soon  pointed  out  that  this  bare 
statement  required  amendment,  for  a  glacier  does  not  move  with 
an  accelerated  velocity,  like  an  avalanche  or  any  other  falling  body. 
The  late  Mr.  Hopkins  showed  experimentally  that  a  mass  of  ice,  if 
its  base  were  slowly  melting,  could  descend  a  slope  of  rock  within 
certain  limits  of  inclination*  without  increase  of  speed,  while  at 
higher  angles  it  slipped  down  in  the  usual  way.  The  late  Professor 
J.  D.  Forbes  maintained,  as  the  result  of  his  careful  investigations 
of  the  glaciers  of  the  Alps,  that  ice  was  really  a  plastic  body,  so 
that  its  movements  resembled  those  of  a  mass  of  hardening  tar. 
But  by  unfortunately  applying  the  epithet  "viscous"  instead  of 
"plastic"  to  the  substance  he  gave  rise  to  misconception,  and 
aroused  opposition.  Professor  Tyndall,  who  was  the  most  active 
assailant  of  his  hypothesis,  brought  forward  experiments  to  show 
that,  while  ice  demeaned  itself  as  a  plastic  body  under  pressure,  it 
failed  so  to  do  under  tension.  So  he  availed  himself  of  the  prop- 
erty of  ice  which  had  been  observed  by  Faraday  and  termed  rege- 
lation — namely,  that  two  masses  of  it  are  frozen  together  if  they 
are  brought  into  contact  when  their  surfaces  are  moist.  In  Profes- 
sor Tyndall's  opinion  a  glacier  was  being  constantly  ruptured  by 
strain,  and  the  broken  pieces,  as  they  slipped  downward,  were 
brought  into  contact  and  cemented  with  new  surfaces;  so  the 
whole  mass  of  ice,  by  repeated  fracturing  and  freezing,  as  it  were 
"shuffled"  down  the  slope.  Lastly,  the  late  Professor  J.  Thomson 
called  attention  to  the  fact  that  the  freezing  point  of  water  is 
lowered  by  pressure/}"  and  suggested  that  the  motion  of  a  glacier 
might  be  explained  in  the  following  way :  Certain  parts  of  a  mass 
of  ice,  resting  as  it  does  on  a  rocky  slope,  must  be  subjected  to  con- 
siderable pressure.  These  accordingly  melt.  This  change  affects 
the  equilibrium  of  the  mass;  parts  formerly  at  rest  can  now  slide 
downward ;  the  water  moves  to  another  position,  is  relieved  from 
pressure,  and  again  passes  into  a  solid  condition,  so  that  the  ulti- 
mate result  is  the  same  as  in  the  preceding  hypothesis. 

*  In  an  experiment  with  a  slab  of  ordinary  sandstone  the  angle  was  about  15°.  De- 
scribed by  W.  Mathews  in  the  "  Alpine  Journal,"  vol.  iv.  p.  413.) 

f  Water,  in  passing  into  ice,  increases  in  volume,  and  if  prevented  from  obtaining 
additional  room  will  remain  fluid  at  temperatures  below  32°  F.  Consequently  a  mass  of 
ice,  if  compressed  into  a  small  space,  returns  to  a  fluid  condition. 


THE    WATER  REGION.  75 

The  claims  of  heat  as  a  motive  force  have  found  fewer  advocates. 
De  Charpentier  was  the  earliest.  He  asserted  that  a  glacier, 
instead  of  being  a  completely  solid  mass,  was  traversed  by  a  num- 
ber of  minute  capillary  tubes,  in  which  water  still  remained  in  a 
fluid  condition.  This  was  affected  by  the  heat  of  the  sun,  being 
expanded  or  contracted  according  to  circumstances.  By  these 
movements  the  mass  as  a  whole  was  affected,  and  their  result  was 
to  impel  it  slowly  downward.  In  this  hypothesis  several  difficul- 
ties are  obvious,  but  one  only  need  be  mentioned — namely,  that 
after  a  most  careful  search  not  the  slightest  trace  of  these  alleged 
capillary  tubes  could  be  detected.  The  late  Canon  Moseley  also 
regarded  heat  as  the  motive  cause,  for  he  thought  that  he  had  dis- 
covered the  following  difficulty  in  any  "gravitation"  hypothesis: 
Different  parts  of  a  glacier  admittedly  travel  at  different  rates. 
Suppose,  then,  that  two  masses  of  ice — say  two  cubic  inches — 
which  at  any  moment  are  in  a  horizontal  line  are  frozen  together. 
As  a  result  of  the  differential  movement  one  of  them,  at  the  end 
of  a  certain  interval  of  time,  is  somewhat  in  advance  of  the  other. 
Particles  on  the  adjacent  surfaces  which  were  once  in  contact  are 
so  no  longer.  "Shearing,"  to  use  the  technical  term,  has  taken 
place,  and  to  produce  this  result  a  force  must  be  exerted.  In  order 
to  ascertain  the  amount  of  this,  Canon  Moseley  devised  a  machine, 
and  his  experiments  demonstrated,  as  he  thought,  that  the  force 
required  to  shear  ice  must  exceed  any  pressure  which  could  result 
from  gravitation.  But  the  motive  power  of  heat  had  been 
impressed  on  his  mind  by  a  practical  experience.  He  was  a  canon 
of  Bristol.  The  lead  upon  the  roof  of  that  cathedral  had  been 
recently  renewed,  and  on  the  southern  side  had  caused  considerable 
trouble  and  expense  by  breaking  loose  from  its  fastenings  and 
"crawling"  downward.  The  reason  for  this  perverse  propensity 
became  evident  on  consideration.  When  a  slab  of  lead  was  heated 
by  the  sun  it  expanded  on  all  sides,  but  in  an  upward  direction  it 
moved  against  gravitation  and  in  a  downward  one  with  it ;  so  that 
the  enlargement  in  the  latter  direction  was  greater  than  in  the  for- 
mer, and  thus  the  mass  as  a  whole  moved  slightly  downward.  But 
when  the  slab  cooled  and  contracted,  the  upper  part  moved  with 
gravitation  and  the  lower  against  it,  so  that  again  a  descent  took 
place.  Canon  Moseley  regarded  a  glacier  as  analogous  to  one  of 
these  sheets  of  lead — as  heated  and  cooled  in  a  similar  way,  and  so 
moving  along  its  bed  by  expansion  and  contraction,  always  in  a 
downward  direction.  The  explanation  is  ingenious,  but  it  does  not 


76  THE   STORY  OF  OUR  PLANET. 

escape  some  of  the  physical  difficulties  which  are  incurred  by  the 
last  one;  and  the  experiments,  which  seem  to  be  fatal  to  the 
"gravitation"  hypothesis,  as  will  be  presently  pointed  out  are  not 
really  conclusive. 

The  hypothesis  advanced  by  the  late  Dr.  Croll  ends  the  list.  He 
looked  upon  glacier  ice  as  consisting  of  molecules  at  a  temperature 
very  little  below  their  melting  point.  The  heat  of  the  s-un,  in  pass- 
ing through  the  mass,  must  be  transferred  from  molecule  to  mole- 
cule. Suppose,  then,  we  consider  the  case  of  a  line  of  them,  A,  B,  C, 
D,  etc.,  in  the  direction  of  movement ;  B  receives  from  the  mass 
above  it,  limited  by  A,  a  certain  quantity  of  heat.  This  is  sufficient 
to  change  it  from  a  solid  to  a  liquid  condition.  The  mass  above  is 
thus  deprived  of  its  support,  and  slips  forward  as  B  is  in  the  act  of 
transferring  the  heat  to  C;  but  now,  as  C  melts,  B  becomes  solid, 
and  another  slip  occurs;  and  so  forth.  Thus  the  whole  mass 
moves  by  a  series  of  molecular  slips.  The  idea  is  ingenious,  but 
not  very  intelligible,  and  it  does  not  appear  to  find  much  favor  with 
physicists. 

As  regards  these  rival  hypotheses,  one  point  is  certain :  that  be 
the  cause  what  it  may,  the  motion  of  a  glacier  is  analogous  to  that 
of  a  plastic  solid.  Streams  of  hardening  pitch,  of  mud,  or  of  lava 
present  us  with  close  analogies — not  seldom  with  exact  reproduc- 
tions— of  the  phenomena  exhibited  by  a  glacier.  It  may  also  be 
observed  that  the  experiments  of  Professor  Tyndall  to  disprove  the 
extensibility  of  ice,  and  those  of  Canon  Moseley  to  ascertain  its 
shearing  force,  are  less  conclusive  than  they  appear  to  be  at  first 
sight,  because  no  account  was  taken  of  the  element  of  time.  It  is 
a  matter  of  everyday  experience  that  a  substance  may  bend  with- 
out breaking,  or  be  changed  in  form  by  forces  comparatively  small 
in  amount  if  only  sufficient  time  be  allowed.  A  stick  of  sealing 
wax  snaps  if  an  attempt  be  made  to  bend  it  suddenly,  yet  if  it  be 
fixed  at  one  end  with  the  other  projecting  from  the  wall  of  a  room 
at  ordinary  temperature,  it  will  assume  a  curved  shape  in  the  course 
of  a  very  few  days.  Experiments  have  proved  that  ice,  in  process 
of  time,  does  bend  by  its  own  weight  without  any  sign  of  fracture,* 
and  in  other  respects  demeans  itself  as  a  plastic  body.  The  diffi- 
culties probably  are  more  apparent  than  real,  and  spring  from  our 
imperfect  knowledge  of  the  molecular  condition  of  bodies.  Solid 
and  fluid  are  antithetic  as  conceptions  of  the  mind,  but  not  as 

*  W.  Mathews,  "  Alpine  Journal,"  vol.  iv.  p.  426. 


THE    WATER  REGION. 


77 


actualities  in  Nature.  For  a  certain  set  of  conditions,  it  is  correct 
to  think  and  safe  to  reason  of  a  substance  as  if  it  were  in  the  one 
state  or  in  the  other;  but  it  by  no  means  follows  that  either  these 
conditions  or  this  method  of  reasoning  are  capable  of  indefinite 
extension.  So,  while  it  may  not  yet  be  possible  to  fix  with  pre- 
cision the  ultimate  cause  of  the  motion  of  a  glacier,  it  seems  safer 
to  say  that  its  demeanor  is  that  of  a  plastic  solid. 

One  result  of  glacier  movement  may  be  described  before  quitting 
this   part  of   the  subject — for  incidentally  it  has  been  mentioned 


FIG.  25.— CREVASSES  IN  A  GLACIER. 

already — namely,  the  formation  of  crevasses  (Fig.  25).  These  are 
produced  by  strains  greater  than  the  ice  can  resist.  For  instance, 
the  difference  in  the  rate  of  movement  of  adjacent  parts  of  a  glacier 
is  greater  near  to  its  sides  than  it  is  at  the  center.  If  the  line  A  B 
(Fig.  26)  represents  a  group  of  particles,  and  if  in  a  certain  time  the 
particle  at  A  has  moved  to  C,  and  that  at  B  to  D,  those  which 
occupied  the  space  A  B  should  now  extend  from  C  to  D ;  but  with- 
out actual  stretching  this  is  impossible,  so  the  strain  is  relieved  by 
fracture.  A  crack  accordingly  opens  somewhere  between  C  and  D 


7 8  THE   STORY  OF  OUR  PLANET. 

in  the  direction  e  f.  Thus  crevasses  are  frequent  near  the  edge  of 
a  glacier,  and  they  point  in  a  general  upward  direction.  But,  fur- 
ther, the  bed  of  the  valley  down  which  the  ice  sheet  descends  is  not 
uniform  in  its  slope;  here  and  there  it  increases,  perhaps  rapidly, 
in  steepness.  Obviously  the  ice  in  passing  over  this  part  is 
strained,  like  a  board  when  it  is  bent  over  the  knee,  so  that  fissures 
open  across  the  glacier.  Irregularities  in  the  form  and  in  the  bed  of 
the  valley,  the  action  of  the  weather,  movements  in  the  broken 
mass,  add  to  the  confusion,  so  that  a  great  "icefall"  is  sometimes  a 
scene  of  the  utmost  complication — a  wilderness  of  yawning  chasms, 
broken  ridges,  and  tottering  towers ;  like  a  cataract  suddenly 


I 


y 

FIG.  26.— DIAGRAM  SHOWING  THE  RATE  OF  MOVEMENT  IN  A  GLACIER. 

frozen,  or,  even  more  correctly,  like  an  ice  avalanche  instanta- 
neously arrested — until  the  bottom  of  the  steep  is  reached,  when 
the  mass  is  slowly  reunited,  the  chasms  are  gradually  closed  up,  and 
the  ice  returns  to  a  more  normal  condition,  though  for  a  con- 
siderable distance  the  "hummocky"  surface  of  the  glacier  is  a 
memorial  of  the  past  disturbance. 

Snow  and  ice  are  direct  agents  of  great  importance  in  modifying 
the  surface  of  the  earth.  That  subject  will  be  noticed  in  a  later 
chapter;  this  one  may  be  ended  by  calling  attention  to  the  impor- 
tant part  which  they  play  in  the  storage  of  water.  The  rain  which 
falls  upon  a  mountainous  district  runs  quickly  down  into  the 
valleys,  and  so  is  carried  away.  The  neighboring  lowlands — espe- 
cially in  a  region  where  the  rains  are  periodic — are  liable  to  alterna- 
tions of  flood  and  drought ;  but  if  the  summits  rise  sufficiently  high 
to  be  covered  with  snow  and  to  generate  glaciers,  these  become 
reservoirs,  from  which  a  perennial  supply  of  water  is  derived.  In 
the  winter,  while  rain  might  be  falling  on  the  lowlands,  snow  would 
be  accumulating  on  the  mountains;  in  a  summer  drought  the  melt- 
ing snow  and  ice  would  fill  the  rivers  and  provide  abundantly  for 
irrigation.  In  the  Apennines,  for  instance,  in  the  summer  season 
the  beds  of  rivers  are  frequently  seen  to  be  dry,  though  they  are 


THE    WATER  REGION.  79 

swept  for  part  of  the  year  by  strong  full  streams,  as  the  pebbles 
which  strew  their  channels  sufficiently  prove ;  yet  in  the  Alps  the 
Reuss  pours  into  the  Lake  of  Lucerne,  and  the  Aar  into  the  Lake 
of  Brienz,  a  much  larger  quantity  of  water  in  July  than  in  Decem- 
ber. The  Reuss  in  the  summer  months  dashes  down  the  rocky 
valley  from  Guttanen  to  Amsteg  in  a  roaring  turbid  torrent,  which 
it  would  be  madness  to  attempt  to  wade;  yet  at  the  end  of 
November  I  have  seen  its  waters  comparatively  clear,  and  so  much 
reduced  in  volume  and  force  that  here  and  there  a  strong  man 
possibly  might  have  stemmed  the  stream  and  crossed  to  the  other 
side.  As  the  snows  melt,  the  waters  rise;  and  thus  the  supply  to 
the  lowlands  is  increased  at  the  time  when  it  is  most  needed. 
Many  a  district  now  parched  and  r.rid  would  be  rendered  compara- 
tively fertile  by  the  addition  of  a  couple  of  thousand  feet  to  a 
neighboring  mountain  range. 


PART  II. 
THE  PROCESSES  OF  SCULPTURE  AND  MOLDING. 


CHAPTER  I. 

THE   WORK   OF   THE   ATMOSPHERE. 

THE  earth's  crust  is  constantly  in  a  state  of  change.  This  is 
most  marked  at  or  very  near  to  the  surface,  though  it  continues  to 
considerable  depths.  But  the  agents  of  external  and  of  internal 
change  are  sufficiently  different  to  make  a  separate  treatment  con- 
venient, so  the  present  part  of  this  book  will  be  restricted,  as  far  as 
possible,  to  the  processes  of  earth  sculpture — viz.,  those  in  which 
the  agents  of  change  act  mainly,  if  not  wholly,  from  without. 

Air  and  water  are  Nature's  principal  carving  tools.  With  the 
former  changes  of  temperature  may  be  considered ;  the  latter  may 
be  conveniently  separated  into  stream  water — such  as  rain,  rivers, 
floods;  into  sea  water — that  is,  the  action  of  waves  and  of 
marine  currents;  and  into  solid  water — that  is,  the  action  of  snow 
and  ice.  But  Nature's  work  is  not  only  destructive;  if  with  one 
hand  she  pulls  down,  with  another  she  builds  up ;  in  her  economy 
transportation  and  deposition  follow  demolition.  The  substance 
dissolved  from  a  rock  is  carried  to  some  other  place,  and  there 
either  is  precipitated  or  enters  into  new  combinations;  the  frag- 
ment broken  away  from  its  surface  is  commonly  borne  along  by 
some  current,  whether  of  air  or  of  water,  until  at  last  it,  or,  more 
strictly  speaking,  a  remnant  of  it,  comes  to  rest,  perchance  hun- 
dreds of  miles  away  from  its  original  position.  The  work  proceeds, 
"without  haste  and  without  rest,"  though  in  this  place  more 
quickly,  in  that  more  slowly,  as  the  forces  of  Nature 

Draw  down  Ionian  hills  and  sow 

The  dust  of  continents  to  be. 

• 

Of  the  agents  of  change  those  directly  connected  with  the  atmos- 
phere produce  the  most  superficial  effects,  and  require  the  briefest 
notice.  First,  as  to  those  due  to  variations  of  temperature — the 
action  of  heat  and  cold.  Obviously  it  is  not  easy  in  practice  to 
separate  them  from  certain  effects  of  water,  for  the  latter  in  freez- 
ing expands  very  suddenly,  and  exerts  great  force.  Hence  a  low 
temperature  produces  much  less  effect  upon  a  rock  when  it  is  dry 

83 


84  THE   STORY  OF  OUR  PLANET. 

than  when  wet,  and  the  latter  condition  is  far  the  more  common. 
Still  in  some  countries  the  rocks,  for  all  practical  purposes,  may  be 
regarded  as  dry,  and  to  the  action  on  these  the  present  chapter  will 
be  restricted. 

When  the  surface  of  a  rock  is  heated  by  the  sun  it  expands ; 
when  the  direct  rays  are  cut  off  by  a  cloud  it  cools ;  it  does  this 
yet  more  when  day  gives  place  to  night.  Experiments  have  been 
made  in  order  to  obtain  accurate  measurements  of  the  expansion 
produced  by  heat  in  different  kinds  of  rock,  and  it  has  been  found 
that  sandstone  expands  more  than  marble,  and  marble  more  than 
granite,  the  coefficient  for  the  first  being  nearly  double  that  of  the 
last.*  As  an  illustration,  it  may  suffice  to  say  that  the  linear 
expansion  of  a  mass  of  average  rock  corresponding  with  a  rise  in 
temperature  amounting  to  100°  F.  may  be  estimated  as  2^  feet 
per  mile.  This  seems  very  slight,  yet  in  a  climate  such  as  that  of 
Rhode  Island,  U.  S.  A.,  it  has  been  found  practically  impossible  to 
make  the  joints  of  coping  stones  perfect.  These  constant  changes 
in  volume  obviously  must  produce  internal  strains,  which  at  last 
will  almost  certainly  break  the  rocks.  The  strains  will  be  more 
irregular  and  more  likely  to  cause  a  fracture  if  one  part  of  the  rock 
is  heated  and  cooled  while  the  rest  remains  at  a  more  uniform 
temperature.  This  is  what  occurs  in  Nature.  The  surface  of  a 
rock  is  most  affected  by  heating  and  cooling;  so  that  in  regions 
where  the  changes  of  temperature  are  considerable  these  alone 
suffice  to  break  up  a  mass,  as  travelers  have  frequently  observed. 
To  quote  only  one  case  as  an  example,  it  was  remarked  by  Living- 
stone that  in  South  Central  Africa  (lat.  12°  S.),  where  the  ther- 
mometer rose  during  the  day  to  137°,  and  fell  by  night  to  42°  F., 
the  rocks  were  being  constantly  fractured  by  strain,  sharp  angular 
fragments  being  detached  which  weighed  from  a  few  ounces  to  a 
couple  of  hundred  pounds.  This  is  by  no  means  an  exceptional 
case;  a  range  of  90°  F.  is  not  seldom  observed  in  South  Australia 
and  in  parts  of  Western  America;  in  the  former  region  it  sometimes 
exceeds  even  100°  F.  No  doubt  much  of  the  loose  sand  and  dust 
so  abundant  in  arid  desert  regions  in  various  parts  of  the  earth  is 
due  to  the  same  cause. 

The  heavier  fragments  lie  where  they  fall.     But  the  wind  can 

*  Colonel  Totten's  experiments  gave  the  following  coefficients  for  each  degree  Fahrenheit : 
Granite,  .000004825  ;  marble,  .000005668  ;  sandstone,  .000009532.  These,  and  numerous 
determinations  (generally  rather  smaller)  by  Mr.  A.  J.  Adie  and  Mr.  T.  M.  Reade,  are 
quoted  in  the  book  of  the  latter,  "  The  Origin  of  Mountain  Ranges,"  ch.  ix. 


THE    WORK   OF   THE  ATMOSPHERE.  85 

deal  with  the  smaller.  It  is  only  on  a  calm  day  that  the  sand  in  a 
desert,  or  above  the  wash  of  the  water  on  the  seashore,  is  at  rest. 
Before  a  brisk  wind  it  is  driven  like  a  cloud.  No  long  journey  is 
needed  to  see  this.  Any  sandy  coast  will  show  it.  At  Southport, 
for  instance,  in  Lancashire,  the  shore  is  very  flat  and  the  sea 
retreats  a  long  way,  leaving  bare  at  low  tide  a  great  expanse  of 
sand.  In  a  high  wind  the  surface  of  this  is  almost  hidden  by  a 
shallow  drift — of  mist,  as  it  seems  from  a  little  distance — which,  as 
it  flows  rapidly  along,  reproduces  on  a  smaller  scale  the  effect  of  a 
sandstorm  in  the  deserts  of  Egypt.  The  grains,  as  they  are  hurried 
forward,  keep  on  striking  one  against  another.  By  this  incessant 
abrasion  their  angles  are  gradually  worn  off,  and  they  are  converted 
into  miniature  pebbles.  A  handful  of  sand  from  the  Libyan  Desert, 
when  examined  with  a  lens,  is  seen  to  be  full  of  rounded  grains, 
while  in  that  which  has  never  been  exposed  to  the  action  of  the 
wind,  such  as  ordinary  river  sand,  hardly  any  of  these  grains  can  be 
found. 

This,  however,  is  not  all ;  the  grains  not  only  impinge  one  upon 
another,  but  also  are  often  dashed  against  projecting  rocks.  These, 
too,  surfer  from  the  incessant  cannonade  of  those  tiny  projectiles. 
Nature  made  use  of  the  "sand  blast"  long  before  man  thought  of 
availing  himself  of  it  for  drilling  and  for  engraving.  When  a  retain- 
ing wall  is  built  by  the  seaside,  in  the  path  of  drifting  sand,  a  few 
years  suffice  to  smooth  the  roughened  surfaces  of  the  hewn  stones. 
Loose  blocks  and  projecting  craglets  on  a  sandy  shore  undergo  the 
same  treatment.  For  instance,  near  Burntisland,  in  Fifeshire,  little 
knolls  of  basalt  crop  out  from  the  sand.  This,  as  it  has  drifted 
before  the  wind,  has  smoothed  and  even  polished  the  hard  rock. 
The  surface,  however,  is  not  perfectly  even,  like  one  worn  by  the 
waves,  nor  is  it  grooved  and  striated,  like  one  over  which,  as  will  be 
presently  explained,  a  glacier  has  passed ;  but  it  is  covered  with 
small  and  extremely  shallow  hollows,  in  shape  something  like  the 
bowl  of  a  teaspoon,  only  longer  in  proportion,  the  narrower  end 
pointing  in  the  direction  of  the  prevalent  wind.  This  structure, 
however,  is  not  always  found ;  but  wherever  sand  drifts  over  rocks, 
there  the  surfaces  are  worn.  Sometimes,  as  in  cases  from  African 
deserts,  the  exterior  of  some  of  the  harder  rocks  is  so  completely 
polished  that  it  appears  as  if  artificially  glazed ;  in  others,  where 
the  material  is  soft,  no  inconsiderable  masses  are  actually  removed 
by  the  friction  of  the  drifting  sand.  Projecting  crags  are  worn  into 
the  strangest  forms;  recesses  in  the  faces  of  cliffs  are  deepened, 


86  THE    STORY   OF  OUR  PLANET. 

possibly  sometimes  even  excavated ;  pinnacles  of  rock  are  undercut 
till  at  last  they  topple  over,  as  a  tree  when  it  is  felled.  In  every 
desert  region — in  all  four  quarters  of  the  globe,  and  in  Australia  no 
less — this  process  is  going  on.  In  Europe  it  is  generally  rare,  still 
it  may  sometimes  be  seen,  as  in  the  strange  forms  of  the  Brimham 
rocks;  but  in  such  arid  districts  as  the  Libyan  deserts,  or  the  plains 


FIG.  27. — WIND- WORN  ROCKS,  YELLOWSTONE  PARK. 

of  Utah  and  Wyoming,  the  results  are  by  no  means  unimportant, 
and  drifting  sand  must  not  be  excluded  from  the  possible  agents  of 
earth  sculpture. 

But  what  becomes  of  the  sand?  Sooner  or  later  it  must  find  a 
resting  place,  though  that  may  be  only  for  a  term  of  years.  If  a 
grain  falls  on  any  spot  where  it  is  sheltered  from  the  wind,  there  of 
course  it  remains.  So  sand  accumulates  in  hollows,  valleys,  shel- 
tered recesses  of  any  kind ;  some  is  blown  into  rivers,  and  is  swept 
away  by  their  currents.  In  sand  from  the  Nile  rounded  grains  are 


THE    WORK  OF    THE  ATMOSPHERE.  87 

frequent.  These,  however,  are  not  formed  by  its  stream,  but  blown 
into  it  from  the  adjoining  deserts;  some,  again,  is  carried  into  the 
sea.  But  not  a  little  accumulates  on  the  land  in  drifts  and  dunes, 
the  latter  being  the  name  commonly  applied  to  low  hills  of  blown 
sand.  How  these  are  formed  is  readily  understood  from  Fig.  28, 
where  the  arrows  represent  the  direction  of  the  blast.  The  process, 
on  a  small  scale,  may  be  watched  on  the  seashore  on  a  windy  day. 
Under  the  lee  of  any  obstacle  (a,  Fig.  28),  be  it  groin  or  post  or 


FIG.  28.— DIAGRAM  SHOWING  THE  FORMATION  OF  A  DUNE. 

bowlder,  a  heap  of  sand  gathers;  even  a  tuft  of  grass  may  originate 
a  tiny  dune,  hardly  big  enough  to  fill  a  tablespoon.  A  bank  may 
also  form,  on  the  windward  side,  aginst  a  groin,  or  a  wall,  or  any- 
thing long  enough  to  arrest  the  advancing  sand,  which  ultimately 
may  overtop  the  obstacle  and  engulf  it  completely.  Such  dunes 
are  accumulations  on  a  small  scale,  but  under  more  favorable 
circumstances  they  attain  to  a  very  considerable  size.  On  the 
British  coast  the  "sand  hills,"  as  they  are  commonly  called,  but  sel- 
dom exceed  30  or  40  feet  in  height,  and  are  limited  in  extent;  but 
the  dunes  in  some  parts  of  the  world  are  far  more  important 
features.  In  the  deserts  near  Khokand  they  rise  to  about  100 
feet.*  "In  the  landes  of  Gascony  a  great  many  dunes  exceed  the 
elevation  of  225  feet.  There  is  even  one,  that  of  Lascours,  whose 
long  ridge,  parallel  to  the  seashore,  attains  261  feet  in  several 
places,  and  raises  its  culminating  dome  to  a  height  of  291  feet.  .  . 
In  Africa,  on  the  low  shores  where  the  ocean  bathes  the  great 
Desert  of  Sahara,  the  enormous  quantity  of  sandy  materials  that 
the  eastern  winds  bring  from  the  desert,  and  which  the  west  wind 
drives  back  to  the  interior,  permit,  it  is  said,  the  dunes  of  Cape 
Bojador  and  Cape  Verde  to  attain  an  elevation  of  from  390  to 
nearly  600  feet."f 

In  all  dunes  the  slope  which  faces  the  wind  is  more  gentle  than 
that  looking  in  the  opposite  direction.  On  the  one  side  of  the  hill 
the  mass  in  front  affords  a  partial  protection  to  that  which  lies 

*  Lansdell,  "  Russian  Central  Asia,"  ch.  xxxiv. 
f  Reclus,  "  The  Ocean,"  part  i.  ch.  xxiv. 


88 


THE  STORY  OF  OUR  PLANET. 


immediately  behind  it,  but  on  the  lee  side  the  sand  can  rest  at  its 
natural  angle  of  repose.  "In  the  landes  of  the  Gironde  the  western 
slope  of  the  dunes  ...  is,  on  an  average,  from  7  to  12  degrees. 
The  eastern  slope,  which  is  that  of  the  descending  talus,  is  from 
29  to  32  degrees;  that  is  to  say,  three  times  as  great."* 

An  isolated  dune  is  generally  crescentiform  in  plan.  It  takes 
this  shape  because  its  ends  advance  more  rapidly  than  the  middle 
part.  Here  the  ridge  is  highest,  so  that  the  sand,  as  it  travels  up 


FIG.  29.— BLOWN  SAND  ADVANCING  ON  CULTIVATED  LAND,  BERMUDA. 

the  one  face  and  down  the  other,  has  a  longer  journey  than  it 
would  have  to  make  near  either  end.  Thus  even  if  the  dune  were 
to  begin  as  a  straight  bank,  with  its  crest  rising  from  the  sides 
toward  the  middle,  it  would,  as  it  advanced,  gradually  assume  a 
crescent  shape,  the  convex  edge,  of  course,  being  turned  to  the 
wind.  "In  the  Desert  of  Atacama,  the  Pampas  of  Tamarugal,  in 
the  plains  of  Texas,  in  the  Sahara  of  Algiers,  in  the  Nubian  deserts, 
and  in  almost  all  the  regions  traversed  by  shifting  sands,  the 
crescent-shaped  dunes  present  such  a  regularity  of  form  that  all 
travelers  have  been  struck  by  it.  The  landes  of  Gascony  also  offer 
remarkable  examples  of  this  semicircular  arrangement  of  the  crest 

*Reclus,  Id.,  ch.  xxiv. 


THE    WORK  OF   THE  ATMOSPHERE. 


89 


of  the  dunes.  In  the  environs  of  Arcachon  and  La  Teste  all 
these  hillocks  have  the  appearance  of  fallen-in  volcanoes,  and  are 
distinguished  by  the  rich  vegetation  of  broom  and  bushes  which 
fill  their  'craters.'  "* 

As  the  dunes  are  formed  of  loose  sand,  they  travel  onward  in  the 
direction  of  the  wind.  Stronger  blasts  than  usual  sweep  up  some 
of  the  material  from  the  exposed  surface  and  drive  it  over  the  crest 
to  fall  down  on  the  lee  side.  So  their  course  is  commonly  land- 


FIG.  30.— TOWER  OF  ECCLES  CHURCH,  A.  D.  1839. 

ward,  and  unless  vegetation  takes  root  upon  the  dune,  and  shields 
its  surface  from  the  wind,  the  fertile  districts  may  be  invaded  by 
the  onward  march  of  the  barren  sand.  In  Bermuda  gardens  and 
woods  are  overwhelmed,  and  the  dead  trunks  of  trees  may  be  seen 
projecting  from  mounds  of  blown  sand.  The  coast  of  Norfolk, 
between  Cromer  and  Yarmouth,  offers  a  remarkable  instance  of  the 
movement  of  a  dune.  Here,  on  the  site  of  Eccles,  a  ruined  belfry 
tower  rises  all  alone  on  the  strand.  At  high  water  it  is  only  a  few 
yards  away  from  the  margin  of  the  sea.  The  walls  of  the  church 
to  which  it  was  attached  are  gone;  only  the  foundations  remain, 
which  are  sometimes  laid  bare  in  places  after  a  violent  storm. 
There  is  now  a  smooth  bank  of  sand  where  folk  worshiped  and 
were  baptized,  were  married  and  were  buried.  Once  the  church 

*  Reclus,  "  The  Ocean,"  part  i.  ch.  xxiii.     See  also  Lansdell,  "  Russian  Central  Asia," 
ch.  xxxiv.,  liv.  etc. 


9°  THE    STORY  OF  OUR   PLANET. 

was  surrounded  by  houses,  once  the  village  was  inclosed  by  fields, 
but  the  sea  has  encroached,  and  as  it  advanced,  the  sand  was  blown 
up  into  dunes,  which  traveled  onward  as  the  vanguard  of  the 
invader.  In  the  year  1839  the  tower  was  buried,  and  its  upper 
part  projected  from  the  mound;  by  1862  it  was  all  but  clear;*  in 
1892  it  rose  from  the  level  strand;  the  dunes  had  passed  to  its 
landward  side,  and  their  outer  slope  began  a  few  yards  from  its 
base.  Nature,  however,  does  not  leave  these  billows  of  sand  to 


FIG.  31.— TOWER  OF  ECCLES  CHURCH,  NOVEMBER,  A.  n.  1862. 

encroach  without  making  any  effort  to  arrest  their  course.  Plants 
there  are  which  can  thrive,  especially  in  temperate  climates,  even  on 
these  arid  wastes.  On  our  own  shores,  and  in  many  parts  of 
Europe,  the  commonest  and  most  useful  is  the  marram  grass 
(Arundo  arenarid).  Though  its  rush-like  leaves  cannot  do  much  to 
arrest  the  wind,  its  long  underground  stems  are  able  to  hold  the 
sand  together.  Thus  aided,  other  plants  also  succeed  in  taking 
root,  and  the  dune,  by  degrees,  becomes  covered  with  vegetation. 
Some  trees,  especially  certain  pines,  contrive  to  grow,  even  to 
flourish,  upon  this  dry  sand,  as  may  be  seen  in  the  pine  woods  of 
Arcachon,  and  the  famous  grove  on  the  Adriatic  shore,  in  the  neigh- 
borhood of  Ravenna. 

In  another  way,  too,  the  movement  of  sand  is  arrested,  though 

*  The  two  sketches  of  the  tower  are  repeated  (by  kind  permission)  from  Sir  C.  Lyell's 
"  Principles  of  Geology,"  ch.  xx.      I  examined  the  locality  in  1892. 


THE    WORK  OF    THE  ATMOSPHERE.  91 

this  happens  but  seldom  in  the  case  of  dunes.  Water  holding 
mineral  salts  in  solution  sometimes  deposits  them  as  it  percolates 
through  the  mass.  The  process  is  initiated  by  some  slightly 
favorable  local  conditions,  but  it  may  continue  when  once  begun 
till  the  whole  mass  is  cemented  together  like  a  bed  of  natural  mor- 
tar. So  solid  does  this  occasionally  become  that  the  downward 
passage  of  water  is  completely  arrested,  and  a  swamp  may  be 
formed  on  the  very  spot  which  was  once  a  dry  plain  of  sand.  This 
has  happened  in  many  parts  of  the  landes  of  Gascony,  but  of  late 
years  extensive  districts  have  been  reclaimed  by  drainage,  and 
rendered  fertile. 

But  if  sand  is  blown  about,  so  also  is  much  finer  dust.  The  dry 
mud  on  the  steppes  around  the  Amu  Daria,  in  the  valley  of  the 
Yellow  River  and  other  parts  of  China,  and  in  the  Bad  Lands  of 
North  America,  is  driven  along  in  dark  clouds,  like  the  smoke  from 
some  vast  furnace.  The  air  is  full  of  these  almost  impalpable  par- 
ticles, stifling  man  and  beast,  and  the  land  is  covered  with  the 
powder,  often  to  a  considerable  depth.  To  this  action  some  geolo- 
gists of  high  repute  have  attributed  a  curious  and  widely  distributed 
mud,  which  is  called  loess  in  parts  of  Europe.  That  deposit  covers 
the  natural  features  of  the  country  like  a  pall  up  to  a  height  of 
some  hundreds,  sometimes  even  thousands,  of  feet  above  the  sea, 
occasionally  accumulating  in  river  valleys  to  so  great  a  depth  as  a 
thousand  feet.* 

Dunes  frequently  exhibit  a  regular  stratification  of  their 
materials,  and  false  bedding  can  be  produced  by  wind  no  less  than 
by  water,  but  obviously  pebbles  will  be  very  infrequent  con- 
stituents, and  will  generally  be  absent.  As  a  rule,  both  these  struc- 
tures are  found  in  sand  hills.  On  the  Picardy  coast  they  can  be 
seen  from  the  train  by  the  traveler  bound  for  Paris  from  Calais ; 
here  certain  beds  occasionally  project  slightly,  as  they  are  more 
coherent  than  the  others.  Like  structures  often  occur  on  the 
shores  of  Britain,  and  are  no  doubt  universal,  but  they  are  some- 
times a  little  difficult  to  find,  because  the  last  layer  of  loose  sand 
hides  all  beneath  it.  Even  where  sections  of  dunes  are  made  by 
storm,  stream,  or  wave,  the  face  of  these  is  quickly  concealed  by 
the  incoherent  material  slipping  from  above.  Dunes,  it  may  be 
added,  are  sometimes  productive  of  change  in  a  more  indirect  way 
than  has  been  already  mentioned.  By  their  advance  they  may  bar 

*Richthofen,  Geological  Magazine,  1882,  p.  293. 


92  THE   STORY  OF  OUR  PLANET. 

the  course  of  a  stream  and  force  it  either  to  change  its  path  or  to 
escape  by  soaking  through  the  sand.  In  temperate  climates  the 
latter  process  very  probably  results  in  a  marsh.  Dunes  may  even 
dispute  possession  with  the  sea,  and  sometimes  obstruct  the  open- 
ings of  estuaries.  Wind  and  water  often  struggle  hard  for  mas- 
tery, but  the  former,  in  the  long  run,  if  it  does  not  triumph, 
obtains  a  partial  success  by  compelling  the  river  to  alter  its  course, 
and  the  sea  to  yield  part  of  its  territory.  The  mouth  of  the  Adour, 
on  the  southwest  coast  of  France,  has  more  than  once  changed  its 
position  during  the  last  three  centuries,*  and  on  the  Gascon  coast 
"the  sea  for  one  hundred  miles  is  so  barred  by  sand  dunes  that  in  all 
that  distance  only  two  outlets  exist  for  the  discharge  of  the  drainage 
of  the  interior. "f  Thus,  though  the  air  is,  in  its  action,  the  most 
superficial  of  the  sculpturing  tools  of  Nature,  it  is  by  no  means  ineffi- 
cient, while  the  transporting  powers  of  the  wind  are  very  far  from 
inconsiderable.  The  lighter  dust  and  the  more  tiny  organisms 
which  it  has  caught  up  are  often  carried  to  very  great  distances. 

The  strange,  almost  unearthly,  glory  that  evening  after  evening 
in  the  late  autumn  of  1883  lit  up  the  sky  after  sunset  was  attrib- 
uted to  the  almost  impalpable  dust,  ejected  some  months  pre- 
viously by  Krakatoa,  which  was  still  floating  in  mid  air  some  twenty 
miles  above  the  surface  of  the  earth.  Dust  falls  on  the  decks  of 
vessels  far  out  at  sea,  and  on  the  lonely  wastes  of  snow  amid  the 
inland  ice  of  Greenland.  Placed  beneath  the  microscope,  it  is 
resolved  into  tiny  chips  of  mineral  and  rock.  Who  can  venture  to 
say  how  long  the  finer  material  ejected  by  a  volcano  or  sucked  up 
by  a  whirlwind  may  not  float  suspended  in  the  atmosphere  before 
it  finally  settles  down  again  on  the  earth,  or  how  far  it  may  travel 
on  its  aerial  course?  The  grain  or  the  germ  which  has  begun  its 
journey  on  the  steppes  of  Asia  or  the  Bad  Lands  of  North 
America,  at  the  crater  of  Cotopaxi  or  from  the  cliffs  of  Chim- 
borazo,  may  bring  it  to  an  end  either  on  some  lone  oceanic  island 
or  in  the  heart  of  a  crowded  city. 

*  During  the  Middle  Ages  the  lower  Adour  flowed  parallel  with  the  sea  for  more  than 
twelve  miles,  and  entered  it  near  Cape  Breton.  Toward  the  end  of  the  fourteenth  century 
this  outlet  was  blocked  by  a  storm,  and  the  river  entered  the  sea  some  nine  miles  further 
north.  The  present  outlet,  partly  artificial,  is  twenty-two  miles  to  the  south,  near 
Bayonne. — Reclus,  "  The  Earth,"  ch.  lii. 

fGeikie,  "  Textbook  of  Geology,"  book  iii.  part  ii.  sect.  i.  par.  i. 


CHAPTER  II. 

RAIN  AND   RIVERS  AS   SCULPTORS. 

RAIN  and  rivers  are  Nature's  most  potent  carving  tools,  running 
water  is  her  most  effective  means  of  transport.  Day  by  day,  night 
after  night,  the  tiny  hammers  of  this  numberless  horde  of  nixies 
and  cobolds  never  cease  to  patter  on  the  rocks,  their  unblunting 
chisels  to  chip  and  hew.  Before  our  eyes,  though  often  they  see  it 
not,  beneath  our  feet,  though  it  is  rarely  perceived,  her  "construc- 
tion trains"  are  running  in  a  never-ending  procession.  This  work 
began  upon  the  earth  before  ever  life  was ;  it  will  continue  so  long 
as  rain  can  fall  and  rivers  can  run. 

Water  exercises  on  rocks  a  twofold  action :  the  one  chemical,  the 
other  mechanical.  It  has  also  a  twofold  end:  destruction  and 
transportation,  the  latter  commonly  leading,  directly  or  indirectly, 
to  reconstruction.  So  far  as  may  be — and  this  is  not  always  possi- 
ble— the  processes  shall  be  separately  described. 

First,  then,  in  regard  to  the  chemical  action.  To  water  no  rock 
is  perfectly  impervious,  by  it  probably  none  is  wholly  unaffected ; 
through  many  it  finds  ready  passage,  on  not  a  few  acts  as  a  rather 
quick  solvent.  The  quantity  of  water  which  a  rock  can  absorb 
before  it  is  saturated  depends  upon  its  constitution,  and,  as  might  be 
expected,  varies  greatly.  In  some  of  the  close-grained  granites  and 
basalts  the  amount  is  very  small,  varying  from  about  one  to  three- 
tenths  per  cent,  by  volume — in  certain  limestones  and  sandstones  it 
will  reach  even  as  much  as  thirty  per  cent.*  Chalk  ranks  among  the 
more  absorbent  of  our  English  rocks.  It  is  at  once  rapacious  and 
miserly,  quick  and  greedy  in  drinking  up  water,  but  very  slow  in 
parting  with  it.  A  piece  of  chalk  63  cubic  inches  in  volume  and  2 
inches  thick  absorbed  12  cubic  inches  of  water  in  a  single  minute 
and  26  inches  in  a  quarter  of  an  hour,  being  then  perfectly  satu- 
rated.f  But  when  left  to  drain  for  12  hours,  it  gave  off  only  one- 
tenth  of  a  cubic  inch  of  water,  and  transmission  was  so  slow  that 

*  Building-stones  of  the  better  class  range  up  to  about  fifteen  per  cent, 
f  Experiment  by   Professor  Prestwich,  "The  Water-bearing  Strata  around   London," 
p.  Go. 

S3 


94  THE   STORY  OF  OUR  PLANET. 

when  8  square  inches  of  its  surface  were  kept  covered  with  half  an 
inch  of  water,  only  six-tenths  of  an  inch  filtered  through  the  block. 
Yet  the  same  quantity  of  sand,  saturated  with  22  cubic  inches  of 
water,  gave  off  by  drainage  in  the  same  time  about  4  cubic  inches, 
and  afforded  such  a  ready  passage  that  water  percolated  through  it 
at  the  rate  of  3840  inches  in  the  12  hours.  But  the  water  as  it 
passes  seldom  fails  to  levy  a  toll  on  the  materials  of  the  rock. 
Many  of  them  are  dissolved  with  comparative  ease,  especially  when 
the  water  contains  a  small  quantity  of  carbonic  acid,  as  is  usual 
with  that  which  has  fallen  as  rain  or  percolated  through  the  soil. 
Geologists  accustomed  to  the  microscopic  study  of  rocks  are 
familiar  with  every  stage  of  the  process  of  decomposition.  They 
know  how  one  group  of  silicates,  from  being  crystal-clear,  becomes 
gradually  tinted  and  ultimately  opaque,  like  a  mass  of  mud ;  how 
another  changes  its  color,  varies  its  optical  properties,  and  assumes 
new  forms ;  how  the  chemical  composition  of  the  rock,  by  a  slow 
process  of  replacement,  is  at  last  so  greatly  altered  that,  for 
instance,  a  mass  of  silicates  and  oxides  may  become  rich  in  car- 
bonates. Basalt,  one  of  the  hardest  of  rocks,  becomes  compara- 
tively soft ;  one  of  the  blackest,  it  changes  color — it  turns  to  some 
shade  of  claret  red  or  brown  or  green  or  gray,  sometimes  even  to  a 
cream  white.  Granite  loses  all  its  strength  and  solidity — the 
quartz,  indeed,  practically  defies  the  foe,  but  as  the  strength  of  a 
chain  is  that  of  its  weakest  link ;  the  mica  yields,  and  the  felspar, 
the  most  abundant  mineral,  changes  to  a  clay.  In  Cornwall,  in  the 
Channel  Isles,  in  Auvergne,  in  many  parts  of  the  world,  the  grains 
of  quartz  can  be  picked  with  the  fingers  out  of  the  surface  of  the 
rotten  granite ;  the  mass  can  be  dug  with  the  spade  to  a  depth  of 
several  yards.  At  Carclaze,  near  St.  Austell,  in  Cornwall,  huge 
pits,  in  which  a  villag?might  be  entombed,  and  perhaps  even  its 
church  tower  be  concealed,  have  been  excavated  in  search  of  tin  ore 
and  china  clay.  This,  however,  must  be  regarded  as  an  exceptional 
case,  for  the  corruption  of  the  rock  was  probably  brought  about  by 
the  passage  of  mineral  springs  containing  certain  corrosive  acids  in 
solution  rather  than  by  the  simple  effects  of  rain  water. 

Constant  dropping,  as  the  old  proverb  runs,  wears  away  stones. 
Rain,  by  chemical  and  mechanical  action,  leaves  its  mark  on  the 
surface  of  rocks.  In  the  course  of  years  the  polish  disappears  from 
columns  of  marble  or  even  of  granite.  The  surface  of  the  former 
rock  soon  loses  all  its  gloss  in  large  towns,  where  the  rain  is  acidu- 
lated by  the  smoke  of  fires  and  the  vapors  of  factories,  though  that 


RAIN  AND  RIVERS  AS  SCULPTORS.  95 

of  the  latter  remains  bright  for  many  decades.  Still  even  in  the 
open  country  these  effects  are  produced,  though  more  slowly.  At 
last  the  smoothed  exterior  of  ashlar  work  becomes  perceptibly 
roughened.  The  inferior  varieties  of  stone,  such  as  certain  red 
sandstones,  crumble  away.  The  cathedrals  of  Chester  and  of  Lich- 
field  have  been,  to  a  great  extent,  refaced,  the  steeple  of  St. 
Michael's  Church,  in  Coventry,  has  been  completely  incased  in  new 
ashlar  work  to  save  it  from  destruction,  and  the  tower  of  St.  John's 
Church,  in  Chester,  became  an  actual  ruin.  Nothing  can  wholly 
withstand  the  action  of  the  atmosphere  and  of  the  rain  (aided,  no 
doubt,  by  changes  of  temperature,  especially  by  frost).  The  surface 
of  the  most  durable  sandstone  becomes  roughened.  Even  blocks 
of  flint  in  the  churches  of  Norfolk  are  dimmed  and  bleached  exter- 
nally, indicating  that  this  most  obdurate  of  rocks  has  been  com- 
pelled to  pay  some  tribute  to  Nature's  solvent  power.  The 
"weathered"  surfaces  of  rocks,  as  they  are  called,  afford  endless 
proofs  of  the  same  common  action.  Obscure  structures,  which 
sometimes  are  scarcely  perceptible  on  freshly  broken  faces,  are 
developed  by  the  quiet,  unceasing,  yet  delicate  process  of  etching 
on  which  Nature's  hand  is  ever  engaged.  About  halfway  up  the 
northern  face  of  Snowdon,  near  the  bridle  path  leading  from  Llan- 
beris  to  the  summit,  a  mass  of  rock  is  passed  which  exhibits  a  num- 
ber of  thin  wavy  streaks  of  a  grayish  white  tint  projecting  slightly 
above  a  darker  surface.  Yet  if  a  fragment  be  broken  off  and  a 
fresh  face  of  the  rock  be  examined  this  structure  at  a  depth  of  a 
few  inches  is  all  but  imperceptible.  In  other  parts  of  Snowdon,  on 
some  of  the  hills  of  Charnwood  Forest  or  of  the  lake  district,  frag- 
ments stud  the  outside  of  the  crags,  and  indicate  to  the  practiced 
eye  that  the  whole  mass  is  composed  of  pieces  of  lava  and  volcanic 
debris.  Yet  on  a  fresh-broken  surface  only  a  faint  mottling  reveals 
the  variety  of  materials  of  which  the  rock  consists.  The  same 
unequal  weathering  produces  the  roughened  surface  of  granite,  so 
welcome  often  to  the  Alpine  climber,  and  contributes  to  the  forma- 
tion of  every  serrate  ridge  and  towering  peak.  Nowhere  is  this 
effect  more  perceptible  than  amid  the  weird  scenery  of  the  Cuchul- 
lin  Hills,  in  Skye,  where  the  augite  crystals  sometimes  stand  out 
full  half  an  inch  from  the  weathered  blocks  of  gabbro.  By  the 
same  unequal  action,  more  particularly  in  limestones,  fossils  are 
developed  and  the  most  delicate  structures  of  organisms  are 
revealed  with  a  perfection  to  which  the  hand  of  man  cannot  attain. 
The  granite  tors  which,  like  ruined  castles,  crown  the  Dartmoor 


96  THE    STORY  OF  OUR  PLANET. 

hills  are  instances  of  the  same  process,  where  it  has  been  carried  a 
little  further.  Joints  originally  divided  the  rock  into  rude  rec- 
tangles ;  of  these  the  faces,  and  still  more  the  corners,  are  attacked 
by  the  weather  till  they  assume  by  degrees  a  more  rounded  outline. 
The  smaller  blocks  rot  away  or  yield  to  the  weight  above;  portions 
of  the  mass  fall,  only  the  more  durable  resisting,  so  that  the  moun- 
tain peak  becomes  a  ruin,  no  less  than  a  fortress  built  by  the  hand 


FIG.  32. — A  GRANITE  TOR  ON  DARTMOOR. 

of  man.  Sometimes  where  one  set  of  joints  dominates  still  more 
curious  forms  are  produced.  A  cliff  near  the  Land's  End  looks  as 
if  built  of  sofa  cushions,  and  one  of  the  shoulders  of  Goatfell,  in 
Arran,  seems  at  a  distance  like  a  pile  of  feather  beds.  In  some 
mountain  regions,  where  thick  masses  of  hard  and  evenly  bedded 
limestone  are  traversed  by  very  regular  joints,  the  resemblance  to 
ruined  masonry  is  even  more  perfect.  No  better  examples  can  be 
found  than  in  the  dolomite  region  of  the  Italian  Tyrol,  where  the 
giant  peaks  often  imitate  with  singular  exactness  ruined  walls  and 
"castled  crags."  (See  Fig.  12,  p.  23.) 

Soil  also,  in  many  districts,  is  a  record  of  the  destructive  action 
of  water,  for  it  is  the  insoluble  or  less  soluble  residue  of  a  rock 
which  has  been  destroyed.  The  top  of  a  limestone  hill  is  often 
bare,  because,  as  the  rock  yields  to  the  elements  and  disappears,  the 
scanty  residue  is  blown  off  by  the  wind,  but  on  the  slopes  below  it 
slowly  accumulates  as  it  is  washed  downward  by  the  rain.  At  first 
a  mere  film  is  formed,  on  which  only  grass  and  scanty  herbage  can 


RAIN  AND  RIVERS  AS  SCULPTORS. 


97 


take  root,  but  at  last  this  becomes  thick  enough  to  support  a  luxuri- 
ant vegetation,  and  even  forest  trees.  The  chalk  downs,  as  in  Sus- 
sex, present  evidences  yet  more  striking.  In  many  places  they  are 
strewn  with  flints.  Sometimes,  no  doubt,  these  are  the  remnants 
of  old  gravel,  and  are  due  to  other  causes;  but  not  seldom  the 
flints  evidently  have  never  taken  a  journey.  They  are  merely  the 
intractable  residue,  once  interbanded  with  masses  of  chalk,  which 
have  been  removed  in  solution.  Nature's  teeth  are  sharp  and 
strong,  but  these  are  awkward  morsels,  so  she  has  eaten  the  peach 
and  left  the  stone  lying  about. 

But  the  corrosive  action  of  water  is  not  confined  to  the  surface; 
it  can  be  followed  up  under  ground.  In  parts  of  the  valley  of  the 
Thames  the  chalk  is  covered  by  sharp  quartz  sand,  which  gives  free 
passage  to  water.  Between  these  two  rocks  a  bed  of  flints,  some- 
times half  a  yard  in  thickness,  commonly  intervenes.  The  flints 
are  exactly  like  those  which  occur  as  thin  bands  in  the  chalk  below, 
except  that  they  are  coated  with  a  kind  of  pigment  of  a  dark  green 
color.  Geologists  agree  that  the  only  possible  explanation  of  this 
bed  is  to  regard  it  as  the  residue  of  a  mass  of  chalk  which  has  been 
eaten  away  by  the  action  of  subterranean  water.  As  the  layers  of 
flint  are  often  separated  by  several  feet  of  pure  chalk,  a  considera- 
ble thickness  of  rock  must  be  represented  by  this  bed. 

"Sand  pipes"  (Fig.  33)  are  another  instance  of  the  same  process. 
These,  though  not  restricted  to  the  chalk,  are  better  exhibited  by 
it  than  by  any  other  kind  of  rock.     The  face  of  a  cutting  in  the 
chalk  is  often  seen  to  be  marked  by  a  brown  streak  running  down- 
ward from  the  top.     This  proves  on  ex- 
amination to  be  a  mass  of  sand  and  gravel. 
It  may  vary  in  diameter  from  some  inches 
to  some  yards;  it  may  extend  downward 
into  the  chalk  for  a  short  distance,  or  it 
may  run  from  the  top  to  the  bottom    of 
the  cutting;  in  form  it  may  be  almost  as 
regular    as  a   well  shaft,    or   it    may   be 
curved  or  conical.     In    the  early  days  of 
geology  these  singular  pits  were  often  at- 
tributed to  the  action  of   whirlpools,  sta- 
tionary tornadoes    of  water,    drilling  out          FlG-  33-— A  SAND  PIPE. 
the  rock   by   the  aid  of  pebbles;  but  to 

this  hypothesis  'their  abundance  was  an  obvious  difficulty,  their 
occasional  curved  form,  to  mention  no  other  objections,  an  insuper- 


f rasa  and  Soil 


98  THE    STORY  OF  OUR  PLANET. 

able  obstacle.  Closer  examination  showed  that  the  stones  in  them 
frequently  lay  with  their  longer  diameters  pointing  downward  ;  that 
where  bands  of  flint  traversed  the  chalk  unworn  blocks  of  this 
material  occurred  at  lower  levels,  also  pointing  in  the  same  direc- 
tion ;  and  that  the  chalk  itself  on  the  walls  of  the  pit  showed  signs 
of  decomposition.  These  facts  may  be  explained  as  follows :  The 
chalk  forrrysrly  was  covered  by  a  thick  layer  of  sand  or  gravel. 
Through  this  water  percolated ;  favored  by  some  accidental 
inequality,  such  as  a  depression  or  small  fissure,  it  attacked  a  par- 
ticular part  of  the  rock  beneath,  gradually  dissolving  a  hollow;  into 
this,  as  it  was  deepened,  the  material  from  above  kept  on  slipping 
down.  It  assumed  a  pipe-like  form,  for  the  work  of  destruction 
would  proceed  at  the  bottom  more  quickly  than  at  the  sides. 
When  a  layer  of  flint  was  reached  the  descent  of  the  mass  for  a 
time  would  be  checked,  but  not  the  corrosive  action  of  the  water, 
for  it  would  pass  downward  through  fissures  in  the  flint.  So  a  kind 
of  chamber  would  be  formed  beneath  the  layer,  but  after  a  time  the 
roof  would  be  crushed  in  by  the  weight  above,  and  the  pipe  once 
more  be  completely  filled.  So  the  work  went  on.  Commonly  the 
gravel  still  remains  on  the  top  of  the  chalk,  but  in  some  cases  it  has 
been  removed  by  natural  processes,  and  at  the  .present  day  these 
pipes  are  the  sole  indications  of  the  mantling  deposit  which  has 
been  stripped  away  from  the  shoulders  of  hills. 

Mineral  springs,  which  will  be  noticed  more  particularly  in  describ- 
ing the  transporting  power  of  water,  are  also  indirect  proofs  of  its 
solvent  effect.  They  contain  in  solution  various  substances.  But 
they  must  be  fed  by  the  rain,  for  a  water  factory  is  not  likely  to 
exist  in  the  interior  of  the  earth.  Rain  water,  however,  as  has  been 
already  stated,  is  practically  pure.  So  these  mineral  salts  must 
have  been  acquired  by  the  spring  water  in  its  passage  through  the 
earth's  crust — or,  in  other  words,  the  latter  must  have  been  deprived 
of  certain  constituents. 

Similar  testimony  to  the  chemical  action  of  water  is  borne  by 
rivers.  They  are  so  largely  fed  by  the  rain  that,  even  if  allowance 
be  made  for  the  contributions  of  springs,  their  water  should  be  almost 
pure.  But  this  is  not  the  case ;  some  mineral  salts  are  always 
detected,  and  a  comparison  of  the  analyses  of  specimens  of  water 
from  different  localities,  as  will  be  shown  in  the  next  chapter,  indi- 
cates that  the  amount  and  the  nature  of  the  substances  in  solution 
depend  on  the  rocks  in  the  districts  which  are  traversed  by  the 


RAIN  AND   RIVERS  AS   SCULPTORS.  99 

The  mechanical  effects  of  water  are  more  obvious  than  the  chem- 
ical. A  heavy  shower  cleans  a  road  from  dust  and  dirt,  fills  the 
gutters  with  muddy  water,  strips  the  earth  from  banks.  Even  the 
raindrops,  as  they  patter  on  the  sand,  leave  their  print  in  tiny  pits. 
Sometimes  these  are  covered  up,  so  that  the  marks  stamped  by  the 


FIG.  34. — FOSSIL  RAIN  PRINTS. 

passing  storm  may  be  preserved  for  countless  centuries.  In  certain 
rock  fossil  rain  prints  (Fig.  34)  are  not  uncommon,  as  in  the  Triassic 
sandstones  at  Grinshill,  in  Shropshire.  Sometimes  it  is  even  possi- 
ble to  conjecture,  from  the  shape  of  the  cavity,  the  direction  in 
which  the  wind  was  blowing,  myriads  of  years  before  man  existed. 
Even  on  the  hardest  rocks  some  effect  is  produced  by  rain,  though 
years  must  elapse  before  this  is  readily  perceptible.  Its  mechani- 
cal action  is  strikingly  illsutrated  by  the  tall  pinnacles  of  stony  clay 
which  are  called  earth  pillars.  These  may  be  found  in  several 
valleys  of  the  Alps,  the  most  remarkable  being  in  the  neighbor- 


loo  THE   STORY  OF  OUR  PLANET. 

hood  of  Botzen,  in  the  Italian  Tyrol,"*  where  they  occur  in  the 
upper  part  of  two  valleys  on  a  mountain  called  the  Rittnerhorn. 
Valleys  already  excavated  in  the  red  felstone  (commonly  called 
porphyry)  have  been  partially  filled  up  with  a  tenacious  clay  which 
contains  many  pieces  of  rock,  large  and  small.  A  glen  has  been 
cut  by  a  mountain  stream  through  the  clay  into  the  rock  below,  and 
on  either  side  it  is  fringed  by  the  earth  pillars.  The  upper  part  of  the 
glen,  on  the  first  glance,  seems  to  be  filled  with  these  rude  obelisks, 


FIG.  35. — EARTH  PILLARS  ON  THE  RITTNERHORN. 


crowded  like  tombs  in  an  overfull  churchyard,  but  on  a  closer 
inspection,  a  method  is  seen  both  in  the  order  and  in  the  shaping 
of  the  pillars.  Now  and  then  one  stands  alone;  indeed,  a  solitary 
giant,  more  than  thirty  feet  high,  may  be  foundf  in  the  pine  wood 

*  Other  familiar  localities  are  near  Stalden,  in  the  Vispthal,  near  Euseigne,  in  the 
Eringerthal,  near  the  path  from  Viesch  to  the  Eggischhorn,  near  Ferden,  in  the  Lots- 
chenthal,  on  the  north  side  of  the  Brenner  Pass,  near  Molines  in  Dauphine  (one  about  70 
feet  high)  near  Sachas,  in  the  same  district,  the  last  also  sometimes  60  to  70  feet  high, 
these  being  somewhat  exceptional  from  the  absence  of  capstones.  (See  Whymper, 
"  Scrambles  Through  the  Alps,"  p.  431 ,  for  a  figure  and  description  of  the  last.)  Examples 
of  the  Botzen  pillars  and  of  that  on  the  Eggischhorn  are  figured  in  Lyell's  "  Principles." 
ch.  xv. 

f  At  least,  it  could  in  1880,  but  as  it  did  not  seem  in  quite  such  good  repair  as  in  1872, 
it  may  be  gone  now. 


RAIN  AND  RIVERS  AS  SCULPTOR'S.;,    j      I  "/;'', ''P*. 

rather  below  the  first  of  the  two  valleys,  but  the  majority  are  con- 
nected, and  many  of  them  form  ridges  of  clay  crested  with  pin- 
nacles. Each  is  usually  capped  by  a  block  of  rock,  like  a  turban ; 
some,  however,  are  bareheaded.  On  this  block  the  existence  of  the 
earth  pillar  depends;  those  which  have  lost  their  caps  lose,  not 
their  heads  only,  but  also  their  bodies.  Here  and  there  the  clay 
slope  is  furrowed  by  a  rill,  but  for  the  most  part  the  "nullahs" 
between  the  ridges  and  the  gaps  between  the  pillars  are  perfectly 
dry  in  fine  weather.  These,  however,  are  wet  enough  after  a  rain- 
storm. 

Three  things  become  pretty  clear  to  a  geologist  after  a  little 
scrambling  among  the  pillars — that  rain  has  cut  the  gullies,  and 
even  furrowed  the  sides  of  the  pillars;  that  the  larger  stones  are 
essential  to  their  formation ;  and  that  the  clay  becomes  very  hard 


FIG.  36. — SECTION  OF  GLEN  WITH  EARTH  PILLARS, 

a,  &,  c,  rock  surface  ;  d,  g,f,  h,  e,  clay  surface  ;  /",  b,  /,  path  of  stream. 

in  drying.  The  process  of  sculpture  was,  roughly,  as  follows :  The 
glen  formerly  was  choked  up  with  this  stony  clay ;  rills  fed  by  rain 
worked  away  at  its  surface,  and  though  the  clay  is  hard  when  dry, 
it  would  quickly  yield  when  damp  to  the  friction  of  the  water,  and 
the  mass  be  plowed  into  a  number  of  furrows.  One  of  these  rills 
in  deepening  its  bed  would  encounter  a  bowlder;  this  would  at  first 
check,  then  gradually  divide,  the  stream ;  and  at  last,  like  a  rocky 
island,  would  separate  it  into  two  currents,  which,  however,  would 
again  be  united  below.  Each  of  these,  after  the  manner  of  cur- 
rents, would  wear  away  the  bank  of  clay  which  faced  toward  the 
stone,  and  would  continue  to  work  outward,  even  when  its  bed  had 
been  cut  down  below  the  level  of  the  obstacle.  Ribs  of  clay  would 
be  left  between  the  rills,  but  as  they  would  be  attacked  not  only 
on  both  sides,  but  also  from  above  by  the  rain,  they  would  gradu- 
ally disappear,  and  the  capstones  would  remain  exalted  on  pin- 
nacles of  stony  clay.  The  rain,  as  their  sides  were  exposed,  would 
beat  upon  them,  and  do  something,  in  trickling  downward,  to 


STORY  OF  OUR  PLANET. 

reduce  their  thickness,  but  the  pillar  for  a  long  time  is  protected 
from  serious  harm  by  the  capstone,  as  by  an  umbrella.  Still  it  is 
very  slowly  attenuated ;  the  capstone  becomes  less  and  less  firmly 
supported,  till  at  last  it  slips  or  is  blown  off.  Then  the  days  of  the 
pillar  are  numbered ;  from  a  pinnacle  it  becomes  a  hump,  and  at 
last  is  wholly  washed  away. 

These  earth  pillars  are  due  solely  to  the  mechanical  action  of 
water,  for  upon  clay  of  this  kind  it  has  no  chemical  effect  of  any 
importance.  In  the  Alps  they  are  seldom  more  than  eight  or  nine 
yards  high,  and  often  rather  less,  but  in  America  they  reach  a  larger 
size.  On  the  flanks  of  Mount  Shasta  they  are  gigantic.  Mr. 
Clarence  King  speaks  of  a  "family  of  pillars  from  one  to  seven  hun- 
dred feet  high,  each  capped  with  some  hard  lava  bowlder  which 
had  protected  the  soft  dtfbris  beneath  from  weathering."*  But 
they  may  be  seen  also  in  miniature.  Where  there  is  a  bank  of 
clay  containing  some  flattish  chips  of  stone — such  as  may  be  found, 
not  seldom,  in  North  Wales — a  careful  search  is  almost  sure  to  dis- 
cover some  tiny  models  of  earth  pillars,  which  perhaps  may  be  as 
much  as  a  couple  of  inches  high,  with  capstones  rather  over  half  an 
inch  in  diameter. 

But,  as  a  rule,  water  acts  both  chemically  and  mechanically. 
Sometimes  the  one  mode  predominates,  as  in  the  making  of  swallow 
holes  and  caves;  sometimes  the  other,  as  in  the  erosion  of  valleys 
and  the  general  task  of  earth  sculpture.  But  in  cave  and  valley 
alike  the  stream  is  making  its  own  bed,  excavating  its  own  chan- 
nel ;  in  the  one  case,  however,  this  is  a  tunnel,  in  the  other  an  open 
cutting. 

On  a  wild  upland  moor  near  Ingleborough  a  stream  has  cut  a 
channel,  some  half  dozen  yards  wide,  through  the  boggy  soil  and 
drift,  down  to  the  underlying  limestone.  This  channel  has  reached 
a  depth  of  some  three  or  four  yards,  when  its  banks  suddenly  curve 
round,  and  it  comes  to  an  end,  as  the  stream  plunges  into  the  lime- 
stone rock,  down  a  vertical  shaft.f  Travelers  are  few  in  this  lone- 
some place,  or  Gaping  Gill,  as  the  pit  is  called,  might  hide  some 
grim  secrets.  Near  the  village  of  Clapham,  rather  more  than  a  mile 
away,  a  pretty  glen  nestles  between  walls  of  gray  limestone.  On 
the  right  bank  a  cliff  is  pierced  at  its  base  by  a  natural  archway, 

*  "  Mountaineering  in  the  Sierra  Nevada,"  ch.  xii. 

f  The  mouth  of  the  principal  shaft  (for  there  is  a  smaller  one,  concealed  behind  a  bowlder) 
is  about  half  a  dozen  yards  broad  and  five  yards  long.  The  shafts  unite  ultimately,  and 
the  depth  to  the  bottom  is  said  to  be  320  feet. 


RAIN  AND  RIVERS  AS  SCULPTORS.  103 

and  some  dozen  paces  further  is  a  much  lower  and  smaller  opening, 
from  which  issues  a  copious  stream.  The  former  of  these  is  the 
entrance  of  the  famous  Ingleborough  caves,  a  series  of  galleries  and 
grottoes  which  run  for  at  least  half  a  mile  into  the  hill.  They  are 
the  work  of  the  stream,  which  for  a  time  was  checked  on  its  down- 
ward progress  by  a  bed  of  rock  harder  than  usual,  and  forced  to 
spend  its  energies  on  excavating  these  caves.  But  at  last  the  floor 
was  pierced,  the  water  began  to  burrow  through  the  softer  rock 
below,  and  is  doubtless  now  at  work  on  a  new  set  of  galleries.  The 
stream  which  has  made  the  Ingleborough  caves  is  the  one  which 
disappeared  down  Gaping  Gill.  This  has  been  proved  by  various 
experiments,  one  of  the  most  convincing  being  afforded  by  Nature. 
Some  years  since  a  violent  storm  broke  over  Ingleborough,  and  a 
torrent  of  water  poured  into  Gaping  Gill.  After  a  time  the  stream 
which  issued  in  the  glen  became  swollen  and  muddy,  till  at  last  its 
channel  was  gorged,  and  the  water  rose  up  through  hidden  pas- 
sages, flooded  the  caves,  and  then  once  more  found  egress  through 
their  portal.  In  the  limestone  districts  of  the  western  border  of 
Yorkshire,  of  Derbyshire,  and  of  Somersetshire  caves  traversed 
by  underground  rivers  are  common.  The  stream  which  flows  out 
beneath  the  grand  archway  of  the  Peak  Cavern  is  said  to  be  the 
same  as  that  which  in  the  Speedwell  mine  plunges  into  a  huge 
fissure,  and  is  struck  still  higher  up  on  its  course  in  the  caves  at  the 
Blue  John  mine.  That  which  flows  through  the  Wookey  Hole 
Cave  in  the  Mcndips  and  emerges  close  by  the  famous  Hyena  Den 
has  been  swallowed  up  near  the  lead  mine  at  Charterhouse.*  The 
springs  which  bubble  up  in  the  gardens  near  the  old  cathedral  at 
Wells  .so  copiously  as  to  make  the  moat  of  the  bishop's  palace  a 
flowing  stream — the  springs  which  doubtless  determined  the  site 
and  gave  the  name  to  King  Ine's  church — restore  once  more  to 
daylight  water  which  has  fallen  as  rain  and  has  been  swallowed  up 
on  the  Mendip  Hills. 

Again  and  again  proofs  of  the  burrowing  habit  of  water  can  be 
obtained  in  limestone  regions.  The  process,  no  doubt,  is  partly 
mechanical,  especially  in  the  lower  part  of  a  swallow  hole,  where  the 
stream  must  fall  with  considerable  plunging  force;  but  it  is  also 

*  This  was  proved  in  a  curious  way.  A  few  years  since  the  company  that  worked  the 
mine  took  to  throwing  refuse  down  a  swallow  hole.  Presently  the  paper  made  at  a  factory 
near  Wookey  Hole,  which  used  the  water,  was  spoiled,  and  the  cattle  which  drank  of  the 
stream  showed  symptoms  of  lead-poisoning.  A  lawsuit  arose,  and  the  company  was 
restrained  by  an  injunction  from  thus  disposing  of  the  rubbish. 


104  THE   STORY  OF  OUR  PLANET. 

chemical,  for  caves  are  very  rare  in  any  but  limestone  districts. 
But  in  such  districts  even  on  the  surface  of  the  ground  proofs  of 
the  corrosive  power  of  water  are  easily  found.  The  jutting  reefs  of 
rock,  all  pitted  and  pockmarked,  the  worn  and  rugged  ridges,  the 
cleft-like  hollows,  where  in  the  Bernese  Alps  the  holly  fern  puts 
forth  its  longest  fronds,  all  tell  of  the  corrosive  work  of  water.  In 
some  parts  of  the  Alps  the  surface  of  the  rock  is  guttered  with 
channels  worn  by  the  rain.  On  a  bare  mountain  region  in  the 
Tyrol,  called  the  Steinerne  Meer,  these  channels  are  often  only  a 
foot  or  two  apart,  and  each  one  ends  in  a  vertical  pipe,  by  which 
the  rain  is  at  once  conveyed  into  the  earth.  So  the  surface  of  the 
rolling  plateau  is  dry  and  desolate;  only  here  and  there  a  chance 
alpine  herb  succeeds  in  striking  in  some  crevice  or  nestling  in  some 
cranny  within  the  drip  of  the  gutters.  By  unknown  outlets,  no 
doubt,  the  hoarded  rainfall  is  again  restored  to  the  light  of  day. 
Springs  are  plentiful  at  the  base  of  the  crags,  as  the  path  drops 
down  toward  the  silent  waters  of  the  Konigs  See.  In  some  districts, 
as  on  the  mountain  south  of  Salzburg  and  near  Hallstadt,  the  great 
limestone  cliffs  are  almost  riddled  with  mouths  of  small  caves  and 
of  natural  drain  pipes.  Sometimes  a  river  can  be  followed  for  some 
distance  under  ground,  like  the  Poik,  which  can  be  traced  near 
Adelsberg  under  the  mountains  for  almost  a  mile,  or  its  presence  is 
indicated  more  indirectly,  as  at  the  dolinas  (swallow  holes)  in  the 
same  district,  which  for  most  of  the  year  seem  to  be  perfectly  dry, 
but  after  heavy  rain  fill  up  and  overflow,  turning  the  whole  plain 
into  a  lake,  until  the  water  again  runs  off  through  subterranean  chan- 
nels. The  surface  of  all  this  region,  in  which  the  famous  Adels- 
berg Caves  are  situated,  and  of  the  mountain  range  on  the  eastern 
coast  of  the  Adriatic,  where  for  league  after  league  the  same  kind 
of  limestone  crops  out,  is  singularly  arid.  Streams  in  other  places 
burst  full  grown  from  the  ground.  So  it  is  with  the  Manifold,  near 
Dovedale,  the  Loue,  and  the  Orbe,  in  the  Jura,  with  the  Siebenbrun- 
nen,  near  the  head  of  the  Simmenthal,  and  many  another.  Even 
the  Mole,  in  Surrey,  is  partially  swallowed  up,  as  is  the  Lesse,  in  the 
limestone  district  of  Belgium,  and  the  water  from  the  solitary  Dau- 
bensee  on  the  Gemmi  Pass  goes  swirling  down  some  small  shafts  at 
the  lower  end  as  it  does  in  the  discharge  pipe  of  a  bath.  Every- 
where in  the  limestone  regions,  be  they  in  any  part  of  the  earth — 
in  Galway  as  in  Derbyshire,  in  the  Jura  as  in  the  Alps,  in  America 
as  in  Europe — swallow  holes,  underground  streams,  and  caves  may 
be  found,  from  the  mere  rock  shelter  like  the  Victoria  Cave  at 


RAIN  AND  RIVERS  AS  SCULPTORS,  105 

Settle  to  the  suites  of  subterranean  halls  at  the  Mammoth  Cave  of 
Kentucky.* 

Valleys,  from  one  end  to  the  other,  bear  testimony  to  the  erosive 
action  of  water.  Formerly  they  were  generally  regarded  as  fissures, 
produced  by  movements  of  the  earth's  crust,  and  much  ingenuity 
was  expended  in  proving  that  the  direction  of  the  valleys  in  an 
upraised  area  corresponded  with  the  rifts  which  would  be  caused 
by  the  strain  to  which  it  must  have  been  exposed ;  but  now  it  is 
generally  admitted  that  while  these  and  other  consequences  of 
earth  movements  may  have  produced  indirect  effects  on  the  courses 
of  streams,  the  rivers  practically  made  the  valleys,  not  the  valleys 
the  rivers. 

Operations  which  Nature  carries  out  on  a  grand  scale  are  often 
reproduced  and  can  be  well  studied  on  a  small  one,  as  in  a  model. 
A  sand  bank,  as  it  drains  dry  after  the  tide  has  retired,  exhibits,  as 
in  a  map,  a  whole  river  system ;  the  furrows  plowed  by  a  storm- 
burst  in  the  slope  of  a  sandy  or  gravelly  moor  repeat  the  outlines 
of  a  mountain  glen.  There  is,  in  short,  not  a  feature  in  the  life  his- 
tory of  a  river  which  cannot  be  found  by  patient  search  in  almost 
any  district  where  the  touch  of  Nature's  finger  is  not  marred  by  the 
hand  of  man.  A  river  may  begin  its  course  in  more  than  one  way. 
Its  history  may  consist  of  more  than  one  chapter.  Valleys  there 
are  which  have  been  engraved,  not  on  smooth  hillsides  or  on  almost 
level  plateaus,  but  upon  a  surface  already  furrowed  by  an  older  sys- 
tem, in  which,  for  some  reason  or  other,  the  streams  have  ceased  to 
flow  and  the  erosive  forces  have  changed  their  lines  of  action.  In 
these  cases  the  complete  history  can  with  difficulty  be  recovered. 
If  a  district,  not  once  only,  has  been  elevated  above  the  sea  and 
depressed  below  it ;  if  the  movements  of  upheaval  and  depression 
have  not  been  uniform;  if  rock  has  been  removed  here  and 
deposited  there,  the  result  may  be  a  tangled  skein  of  evidence  very 
hard  to  unravel.  Still  even  in  such  cases  the  history  of  the  last 
and  most  conspicuous  valley  system  can  generally  be  determined. 
We  may  be  in  doubt  as  to  the  exact  process  by  which  the  moun- 
tain peaks  were  originally  defined,  but  we  can  generally  trace,  out 
the  history  of  most,  if  not  all,  the  valleys.  They  often  differ  in 

*  Professor  Shaler  ("  Aspects  of  the  Earth,"  p.  109)  estimates  that  "  within  a  section  of, 
say,  ten  square  miles,  and  a  thickness  of  300  feet,  in  which  lies  the  Mammoth  Cave,  there 
are  probably  in  the  known  and  unknown  galleries  more  than  200  miles  of  ways  large 
enough  to  permit  the  passage  of  a  man,  besides  what  is  probably  a  greater  length  of  smaller 
channels." 


Io6  THE   STORY  Of  OUR  PLANET. 

their  origin.  Sometimes  the  first  stage  is  hardly  marked,  as  when  a 
stream  begins  from  a  snow  bed  or,  as  not  seldom  in  our  own  island, 
from  a  boggy  upland.  For  a  time  it  trickles  down,  soaking  through 
mossy  banks  or  even  sinking  for  a  brief  space  into  shelving  screes. 
Then,  as  the  rivulets  gather  together  into  a  rill,  and  this  acquires 
strength  as  it  runs,  it  begins  to  furrow  the  slopes;  a  little  lower 
down,  perchance,  some  outcropping  ledge  rather  harder  than  its 
neighbors  for  a  moment  checks  the  stream ;  it  leaps  this  obstacle 
and  strikes  down  upon  the  underlying  softer  rock.  By  this  plung- 
ing motion  a  Avaterfall  is  begun  (Fig.  37).  If  the  slope  be  rapid, 
and  the  structure  of  the  rock  permit,  the 
stream  may  descend  in  a  series  of  leaps. 
But  be  the  leap  only  that  of  a  rill  and  for 
a  few  inches,  or  that  of  the  whole  St. 
Lawrence  for  the  fifty  yards  of  Niagara, 
the  cause  of  the  waterfall  is  the  same — a 
harder  ledge  or  mass  projecting  in  the  bed 
of  the  river  and  overlying  some  softer  rocks. 
Sometimes,  however,  a  glen  has  a  more 

definitely    marked     beginning.     When   the 
FIG.  37. — A  WATERFALL.         ,     n  ..  T-       i-  i      i 

shallow  valleys  on   our   English  downs  arc 

traced  up  to  their  head  they  are  often  found  to  start  from  a  bowl- 
like  hollow.  Its  walls  in  some  regions  are  rocky  and  steep,  at  times 
almost  vertical.  There  exist  natural  apses,  sometimes  almost 
amphitheaters,  on  a  large  scale  and  on  a  small ;  the  great  corries  in 
the  Cuchullin  Hills  or  in  the  heart  of  the  Highlands,  the  huge 
"cirques" — recesses  almost  surrounded  by  precipices — such  as 
Gavarnie  and  Troumouse  in  the  Pyrenees,  the  Fcr  a  Cheval  or  the 
Creux  de  Champs  in  the  Alps — are  often  reproduced  on  a  small 
scale  in  the  beds  of  gravel,  sand,  and  drift  in  our  own  country. 
Under  the  slopes  of  the  East  Binn  at  Burntisland  some  years  since 
was  a  perfect  model  of  a  corrie ;  it  was  only  four  or  five  yards 
across,  but  illustrated  completely  the  process  by  which  such  hol- 
lows are  formed.  The  sides  were  furrowed  by  the  rain  runlets, 
which,  working  on  the  soft  ashy  rock,*  had  gradually  excavated,  as 
they  converged  toward  a  common  center,  this  bowl-like  hollow, 
from  which  their  water  had  escaped  by  a  single  channel  at  the  lower 
end.  Sometimes,  also,  in  the  sands  of  Hampshire  or  of  the  Isle  of 


*  The  hill  is  a  mass  of  coarse   ash  or  "  agglomerate  "   connected  with  a   very  ancient 
volcano,  the  crater  of  which  has  long  since  disappeared. 


RAIN  AND  RIVERS  AS  SCUT.PTORS. 


107 


Wight,  the  model  of  a  cirque  may  be  seen  produced  by  the  rills  of 
rain.  The  larger  corries  and  the  greater  cirques  are  the  work  of 
more  powerful  streams ;  those  in  the  latter  case  are  commonly  fed 
by  permanent  snow  beds  resting  on  the  upper  ledges  of  the  moun- 
tain. The  strongly  marked  recesses  are  less  common,  both  on  the 
small  scale  and  on  the  large,  but  almost  every  valley,  if  it  does  not 
actually  die  out  on  the  hillside,  ends  in  a  more  or  less  bowl-shaped 
hollow. 

As  the  stream  descends  the  mountain  slope  and   increases  in 


FIG.  38. — DIAGRAM  OF  A  CIRQUE,  SURENEN  PASS. 

A,  Peaks  in  clouds  ;  B,  limestone  cliffs  ;   C,  shaly  slopes  ending  in  D,  harder  rock  furrowed  by  streams  ; 
E,  limestone  cliffs,  slightly  grooved  ;  F,  talus  heaps  on  floor. 

volume,  the  glen  deepens.  Its  shape  depends  on  more  than  one 
factor,  and  hereafter  must  be  considered  in  detail ;  for  the  present 
it  is  enough  to  say  that,  as  the  slope  is  regarded  from  a  distance, 
the  scar  on  its  surface  can  be  seen  to  widen  and  deepen,  as  if 
Nature's  claw  had  been  driven  into  the  earth  with  ever-increasing 
strength. 

Yet  lower  down  streams  unite  their  waters,  and  glens  coalesce 
into  a  valley.  That  may  become  deeper,  or  it  may  become  broader, 
according  to  circumstances;  but  glen  joins  glen  and  valley  unites 
with  valley,  till  at  last  their  confluent  waters  sweep  out  into  the  low- 
lands. Then  the  hills  retire,  the  river  plain  between  them  widens 
out,  till  in  some  cases  all  trace  of  a  valley  is  lost.  In  fact,  as  will 
be  presently  explained,  a  river  at  last  often  ceases  to  erode  and 
begins  to  deposit— instead  of  deepening  it  actually  raises  its  bed. 

The  forms  which  a  river   valley  may  assume   mainly  depend    on 


io8  THE   STORY  OF  OUR  PLANET. 

two  conditions:  the  erosive  force  of  the  stream — the  joint  effect  of 

its  volume  and  of  its  velocity — and  the  nature  and  structures  of  the 

rocks,  whether  hard  or  soft,  whether  homogeneous  or  the  reverse, 

together  with  the  directions  of  the  dominant  planes  of 

J  weakness. 
A    rapid    stream   takes   a  straight   course;  a  slow 
one  meanders  along  in    curves.       If  the    fall  be  not 
less   than  ten   feet    a    mile,  the    channel  is   perfectly 
straight ;  if  the  fall  be  only  three    inches,    the  path 
is  a  semicircle.*     The  windings  of  a  little   stream  are 
FIG.  39.— TER-  frequent  and  small ;  those  of  a    large  stream  may  be 
RACED  CUFF,   measured  by  miles.     In  the  bed    of  one    of   our   flat 
A'  ""hale"" ;  P>  English  valleys  a  brook  will  make  several  twists  in  the 
compass  of  a  single  field,  while  in  the  channel  of  the 
Mississippi  two  points  a  few  hundred  yards  apart   by  land  may  be 
separated  by  ten  miles  or  more  of  river  travel.     Dealing  first  with 
the  straight  courses,  if  the  stream  be  strong,  the   rocks  hard  and 
resistant,  it  cuts  gorges.     Such  may  be  seen  occasionally  among  the 
British  hills,  but  here  they  are  on  a  small  scale ;  they  are  commoner 
and  on  a  grander  scale  in  the  Alps.     The  gorge  of  the  Visp  near 
Zermatt,  of  the  Trient  near  Vernayaz,  in  crystalline  rocks,  of  the 
Tamina  near  Pfafers  (Fig.  41)  and   the   Hinter  Rhein  at   the  Via 
Mala,  in  slaty  rocks,  of  the  Kirchet  on  the  Aar  and  of  Sottoguda 
near  Caprile,  in  calcareous  rocks,  are  among  the  finest   examples. 
If  the  rock  be  homogeneous,  and  the  planes  of  bedding,  cleavage, 
or  jointing  neither  too  numerous  nor  inclined  at  too  acute  angles  to 
the  horizon,  the  cliffs  will  be  straight  and  steep,  the  gorge  almost 
like  a  fissure  in  the  earth's  crust — as  once  it  was  erroneously  held 
to  be.     If,  however,  the  rocks  consist  of  alternate  layers  of  soft  and 
hard,  the  former    will  wear    away    more 
quickly,  not  only  under  the  action  of  the 
stream    cutting  laterally,  but  also  under 
that  of  the    weather  working  upon    the 
surfaces    exposed  in    the   walls.     These, 
then,    cannot     remain    vertical,     but     in 
receding    assume  a  terraced    form,  crag     FlG-  40.— GORGE  IN  SLOPING 

oEDS. 

and  slope  alternating  in  accordance  with          flfl>  Bedding;  /./..jointing. 
the    characters    of   the    beds   (Fig.    39). 

Again,  if  the  rock  be  traversed  by  divisional  planes,  a  gorge  can  be 
cut  so  long  as  the  blocks  lie  horizontally,  because  they  are  then  in 

*J.  Fergusson,  Quarterly  Journal  of  the  Geological  Society,  vol.  xix.  p.  321. 


RAIN  AND  RIVERS  AS  SCULPTORS. 


109 


a  stable  position,  like  the  stones  in  a  wall ;  but  if  the  planes  slope 
to  the  horizon,  the  blocks  are  in  this  position  on  one  side  of  the 
cutting  only,  on  the  other  they  will  slip  downward  and  fall :  thus 
the  cliff  on  one  side  of  the  gorge  is  nearly  vertical,  on  the  other  it 
becomes  a  slope  (Fig.  40). 

Gorge-like  valleys  of  some  magnitude  can  be  found  in  more  than 
one  part  of  Europe,  such  as  Les  Goulets,  in  the  outer  Alps,  south- 


FIG.  41. — THE  GORGE  OF  THE  TAMINA,  PFAFERS,  SWITZERLAND. 


west  of  Grenoble,  and  the  valley  of  the  Sarca  below  Tione,  in  the 
mountain  district  of  the  Brenta  Alta.  But  no  more  wonderful 
instance  of  the  erosive  action  of  water  exists  on  the  earth's  surface 
than  that  afforded  by  the  caflon  district  of  Colorado.  The  basin 
drained  by  this  river  is  a  vast  plateau  extending  from  the  western 
side  of  the  Rocky  Mountains  to  the  head  of  the  Gulf  of  California. 
For  nearly  five  hundred  miles  the  river  flows  at  the  bottom  of  a  gorge 


HO  THE   STORY  OF  OUR  PLANET. 

from  three  to  six  thousand  feet  below  the  level  of  the  plateau.  The 
scenery,  so  admirably  illustrated  by  the  Geological  Survey  of 
America,  reveals  to  the  practiced  eye  a  marvelous  instance  of  earth 
sculpture.  The  traveler,  as  he  rides  across  the  plateau,  may  halt 
on  the  edge  of  a  crag  overlooking  a  broad  valley.*  Its  floor  is 
several  miles  wide;  it  is  bounded  by  steeply  terraced  walls,  some 
two  thousand  feet  in  height.  Here  they  project  in  bastions  or 
sharp  salients;  there  outlying  masses  like  ruined  forts  rise  from  the 
plain  belieath.  The  plateau  on  either  side  is  furrowed  by  valleys, 
some  of  them  waterless,  others  still  traversed  by  streams,  all  con- 
verging to  this  huge  trench  which  is  so  like  the  dried-up  bed  of  a 
river.  This,  however,  on  closer  inspection  is  seen,  like  the  plateau 
above,  to  be  severed,  but  by  a  gorge,  the  walls  of  which  descend 
yet  more  steeply  than  the  escarpments  bounding  the  upper  trench, 
for  they  plunge  down  in  places  almost  vertically  for  full  three  thou- 
sand feet.  At  the  bottom  flows  the  river — a  swift,  strong  stream. 
These  massive  walls,  like  the  escarpments  above,  are  gashed,  though 
yet  more  sharply,  by  lateral  ravines,  down  which  it  is  possible  occa- 
sionally to  descend  to  the  level  of  the  Colorado,  but  its  waters  not 
unfrequently  for  dozens  of  miles  are  quite  inaccessible.  The  hunter 
might  shoot  a  stag  across  the  chasm,  but  it  would  take  him  more 
than  a  day's  journey  to  get  the  venison.  The  formation  of  these 
vast  gorges  has  been  rendered  possible  by  a  combination  of  favora- 
ble circumstances.  The  whole  plateau  is  built  up  of  masses  of  fairly 
hard  standstone  and  limestone,  with  but  little  of  softer  materials, 
disposed  horizontally  with  curious  regularity,  like  courses  of  Titanic 
masonry;  and  it  rests  on  a  foundation  of  solid  granite,  into  which 
sometimes  the  river  has  cut  a  trench  for  as  much  as  a  thousand 
feet.  The  rainfall  in  the  immediate  neighborhood  is  slight,  so  that 
the  elements  can  do  little  to  destroy  the  edges  of  the  trench  and 
diminish  the  steepness  of  the  walls;  but  it  is  heavy  on  the  head 
waters  of  the  river,  for  such  a  work  as  this  could  only  be  done  by 
powerful  cutting  tools. 

As  a  river  begins  to  wind,  a  valley,  as  a  rule,  begins  to  change  its 
outline.  The  erosive  force  of  the  water  being  diminished,  the 
effects  of  the  elements  become  relatively  more  important.  The 
sides  are  no  longer  vertical,  but  begin  to  slope;  the  valley  in  a 
cross  section  takes  the  form  of  a  V  instead  of  an  elongated  U. 
This,  however,  is  not  all.  It  is  but  seldom  that  the  two  arms  of  the 

*  Such  as  appears  in  the  upper  part  of  the  picture  (Plate  III.). 


RAIN  AND  RIVERS  AS  SCULPTORS. 


ill 


V  are  equally  inclined  to  the  horizon.  Planes  of  separation  in  the 
mass  of  the  rock  may  bring  this  about,  as  already  described,  but 
another  and  a  more  general  cause  is  now  at  work.  In  all  rivers  the 
water  at  the  surface 
moves  more  rapidly 
than  that  in  contact 
with  the  bed,  for  fric- 
tion checks  its  speed ; 
the  water  in  the  middle 
outstrips  that  near  the 
sides.  But  when  a  river 
winds,  the  median  line 
of  the  channel  only  for 
a  moment  corresponds 
with  that  of  quickest 
motion.  Suppose,  for 
instance,  the  course  of 
a  stream,  represented 
by  the  lines  P  A  R,  Q 
B  s,  in  the  annexed 
diagram,  to  change  at 
the  points  A  B  from  a 
straight  line  to  a  curve, 
the  line  of  quickest  mo- 
tion, which  is  parallel 
to  A  P,  B  Q,  will  pass 
through  c,  the  middle 
point  of  A  B.  This 
line,  below  c,  will  not 
curve  in  correspondence 
with  the  banks  so  as  to 
divide  the  space  be- 
tween them  equally, 
but  it  will  be  nearer 
to  the  bank  PAR 
than  to  Q  B  S,  because, 
in  conformity  with  the 
well-known  law  in  dy- 
namics, "a  body  in  mo- 
tion will  continue  in 
motion  uniformly  and  FlG-  42.— IN  THE  BED  OF  A  CASON. 


112  THE   STORY  OF  OUR  PLANET. 

in  a  straight  line  until  acted  upon  by  some  external  force."  So  the 
line  of  quickest  motion  would  continue  to  be  a  straight  one  were  it 
not  for  the  resistance  of  the  bank  PAR,  and  the  curve,  which  it 
actually  does  follow,  lies  rather  on  that  side  of  the 
channel.  Thus  beneath  this  bank  the  water  flows 
more  swiftly,  and  its  erosive  effect  is  greater  than 
on  the  opposite  side.  In  a  winding  river,  as  every 
boy  knows,  the  water  is  deeper  on  the  outer  side 
of  a  bend — there  he  will  find  the  best  place  for  a 
header;  on  the  other  the  bottom  will  shoal,  so  that 
a  child  might  paddle  on  the  one  side  of  the  stream 
FIG.  43 "DIAGRAM  while  on  the  other  he  would  be  out  of  depth  at 

°nce'     S°    'lt    is   als°    with  the   valley-     Its    sl°Pes 
descend    steeply  toward    the   convex   part    of  the 

river:  they  shelve  down  more  gently  toward  the  concave  side. 
As  the  river  oscillates  backward  and  forward,  the  deeper  part 
of  its  bed  changes  its  position  from  side  to  side;  so  also  do  the  cor- 
responding slopes  of  the  valley.  This  is  generally  obvious  enough. 
In  England  it  is  more  conspicuous  in  the  minor  valleys;  in  those 
traversed  by  the  more  important  rivers  the  water  no  longer  occu- 
pies the  whole  breadth  of  the  valley,  but  meanders  over  a  flat  plain, 
often  taking  a  course  altogether  different  from  that  which  it  fol- 
lowed when  engaged  in  excavation. 

The  Meuse,  in  its  passage  through  the  Ardennes,  exhibits  some 
very  striking  illustrations  of  the  connection  of  the  slopes  of  a  valley 
and  the  curves  of  a  stream.  Between  Deville  and  Revin,  two  town- 
lets  on  its  banks,  the  river  swings  to  and  fro,  forming  three  great 
loops,  and  carves  a  deep  trench  in  a  forest-clad  plateau  of  slaty 
rock.  The  side  of  the  valley  facing  the  apex  of  one  of  these  loops 
is  nearly  precipitous,  and  the  woods  descend  almost  to  the  level  of 
the  water,  but  the  point  of  land  thus  encompassed  shelves  much 
more  gently  down,  and  is  cultivated  up  to  the  level  of  the  plateau. 
By  following  the  serpentine  curve  of  the  river  the  steep  and  the 
gentle  slopes  may  be  seen  alternating  in  correspondence  from  side 
to  side  of  the  valley.  At  Revin  itself  the  town  comes  twice  to  the 
water  side,  for  it  extends  across  a  neck  of  land  perhaps  350  yards 
wide,  while  the  river  flows  round  a  headland  hill,  making  a  journey 
of  some  2^/2  miles.  The  current  obviously  presses  upon  both 
sides  of  this  neck,  and  if  man  had  not .  interfered  by  choosing 
this  convenient  spot  as  the  site  of  Revin,  the  neck  would  ultimately 
be  carved  away  and  the  river  make  a  short  cut  by  insulating  the 


BIRD'S-EYE    VIEW    OP    THE    CARONB    OP    COLORADO. 


RAIN  AND  RIVERS  AS  SCULPTORS.  113 

headland.  In  some  countries  where  the  river  is  strong  and  the 
rock  is  weak  these  "cuts-off"  are  not  unfrequently  found ;  the  cur- 
rent, of  course,  abandoning  the  old  channel,  which  thus  becomes 
"dead  water."  This  by  degrees  is  separated 
from  the  bed  of  the  running  stream  by  the  de- 
posit of  silt  and  by  the  growth  of  vegetation. 
These  form  a  natural  embankment,  and  convert 
the  old  course  of  the  river  into  a  horseshoe-shaped 
lake.  "In  the  basin  of  the  Mississippi,  the  Am- 
azon, the  Ganges,  the  Rhone,  and  the  Po  there 
are  a  considerable  number  of  these  circular  lakes. 
We  may  trace  out  with  the  eye,  as  it  were,  three 

rivers,  one    of    which,   active   and    living,    flows     FlG-  44-— DIAGRAM 
...  ,  OF  WINDING  RIVER. 

without  interruption  from  its  source  to  the  sea, 

while  the  two  others  on  either  side  are  become  'dead  water.'  The 
remains  of  these,  scattered  all  along  the  existing  river,  still  point  to 
the  spot  where  once  extended  its  ring-like  windings.  In  conse- 
quence of  the  alternate  shiftings  of  position,  the  valley  is  always 
much  wider  than  its  river,  and  along  its  circuitous  path  winds  the 
continually  changing  bed  of  the  existing  stream.  In  some  parts  of 
its  course  the  Po  only  takes  about  thirty  years  in  forming  and 
destroying  each  of  its  meanders."* 

In  districts  where  the  rocks  are  disposed  in  layers,  and  thick 
masses  of  fairly  strong  and  homogeneous  materials  predominate, 
terraced  walls  characterize  every  valley  and  support  every  plateau. 
In  the  British  Isles  examples  of  this  structure,  except  on  a  very 
small  scale,  can  hardly  be  found.  They  are  at  their  grandest  in 
the  Colorado  district,  as  already  mentioned,  and  in  other  parts 
of  Western  North  America.  In  the  Pyrenees,  especially  on  the 
Spanish  side,  good  instances  may  be  sometimes  seen ;  but  perhaps 
the  best,  on  the  whole,  in  Europe  may  be  found  among  the  dolo- 
mite mountains  of  the  Italian  Tyrol.  The  Schlern,  the  Sella  Spitz, 
the  Rosengarten  group,  with  other  peaks  of  less  fame,  are  excellent 
instances  of  the  fortress-like  masses  which  have  been  carved  out  of 
beds  of  rock  which  once  extended  over  a  much  wider  area. 

Escarpmentsf   are    less   obviously,    but    not    less    certainly,  the 

*  Reclus,  "  The  Earth,"  ch.  xlix.,  where  two  plates  are  given,  illustrating  part  of  the 
course  of  the  Mississippi,  with  its  "bayous"  or  "  cuts-off." 

f  This  word  denotes  the  steep  or  precipitous  faces  shown  by  a  mass  of  rock  as  it  crops 
out  of  the  earth  in  a  mountainous  or  hilly  district.  Obviously  the  crags  of  a  terraced 
plateau  are  escarpments,  but  the  term  is  generally  applied  to  the  less  regular  instances, 
where  the  beds  do  not  lie  horizontally. 


H4  THE   STORY  OF  OUR  PLANET. 

results  of  the  same  erosive  action  of  water.  The  steep  face  of  the 
Cotswolds  overlooking  the  valley  of  the  Severn,  the  rapid  plunge 
from  the  crest  of  the  North  Downs  to  the  level  of  the  Weald,  are 
two  among  many  examples.  Formerly  escarpments  were  sup- 
posed, like  the  "white  walls"  of  England,  to  be  the  work  of  the  sea, 
but  it  became  evident,  on  closer  examination,  that  this  idea  could 
not  be  maintained.  When  an  escarpment  is  traced  across  the  coun- 
try, it  is  found  to  follow  the  outcrop  of  a  particular  bed  of  rock, 
and  its  face  rises  and  falls  correspondingly  with  any  flexures  in  the 
latter.  Not  so  with  an  old  sea  cliff.  As  a  rule,  its  face  remains  at 
the  same  height  above  the  Ordnance  datum,  and  it  cuts  across 
different  layers  of  rock  in  succession.  In  the  case  of  the  Weald, 
there  is  no  reason  to  suppose  that  any  part  of  it  has  been  overflowed 
by  the  sea,  except,  perhaps,  in  the  vicinity  of  the  coast,  since  the  time 
when  its  present  structure  was  first  defined.  The  whole  valley,  or 
rather  the  system  of  valleys,  which  make  up  this  garden  of  Southern 
England,  has  been  the  work  of  fresh  water  in  some  form  or  other. 
Some  time  after  the  chalk  was  deposited  the  crust  of  the  earth 
must  have  been  slowly  upheaved  so  as  to  form  an  egg-shaped  dome, 
the  longer  axis  of  which  extended  at  least  from  the  western  side 
of  Hampshire  to  some  distance  east  of  the  railway  between  Calais 
and  Boulogne.  As  this  mass  gradually  rose,  its  crest  would  be 
planed  away  by  the  waves;  very  possibly  the  chalk  may  have  been 
wholly  removed  from  its  central  part,  and  the  underlying  clay — 
called  the  gault — laid  bare.  No  sooner  had  the  waves  retired  from 
any  part  of  the  region  than  a  new  set  of  foes  would  rush  to  the 
attack,  and  its  surface  be  worn  by  rain  and  by  rivers.  As  the  dome 
continued  to  rise,  streams  would  run  down  its  slope,  and  furrows  be 
cut  along  the  quickest  lines  of  descent.  But  between  the  masses 
of  more  resistant  rock,  as,  for  instance,  between  the  chalk  of  the 
Caterham  Downs  and  the  Lower  Greensand  of  Nutfield  ridge,  and, 
again,  between  the  latter  and  the  hilly  central  district,  lie  thick 
beds  of  softer  clay,  which  after  a  time  would  be  exposed  to  the  sur- 
face, even  if  they  were  not  at  first.  On  these  the  running  water 
would  act  more  rapidly;  the  rain  which  fell  upon  the  areas  between 
the  main  channels  of  drainage  would  be  discharged  into  them  by 
lateral  streams.  These  would  excavate  a  course  for  themselves  in 
the  soft  clay,  and  thus  catch  the  water  from  the  adjacent  slopes  of 
the  harder  beds  on  either  side.  In  this  way  lateral  valleys  would 
be  formed,  of  which  the  floors  would  be  deepened  pari  passu  with 
those  of  the  main  channels,  and  the  heads  would  be  cut  back  into 


RAIN  AND  RIVERS  AS  SCULPTORS.  115 

the  clay  on  either  side  until  they  met.  As  these  valleys  would 
descend  very  gently,  their  beds  would  be  widened  by  the  meander- 
ing streams,  while  those  which  radiated  outward  from  the  central 
part  of  the  dome  would  be  steeper,  and  so  comparatively  narrow. 
When  a  geological  map  of  the  Weald,  on  a  small  scale,  is  examined, 
the  connection  between  its  river  valleys  and  its  rocks  is  readily  seen  ; 
but  on  the  ground  the  minor  irregularities  due  to  the  interference 
of  channels,  the  changes  in  the  course  of  streams,  the  action  of  the 
rain,  and  a  hundred  local  causes  of  complication,  often  give  rise  to 
considerable  difficulties  in  interpreting  the  structure.  Still  these 
diminish  as  the  eye  gains  experience,  and  most  of  them  yield  to 
patient  work,  so  that  no  reasonable  doubt  can  exist  as  to  the 
general  history  of  the  development  of  the  physical  features  of  the 
Weald.*  In  many  places  indications  of  the  process  of  sculpture 
still  remain,  like  workmen's  tool  marks  in  a  deserted  part  of  a 
quarry.  There  are  old  beds  of  gravel,  often  at  considerable  heights 
above  the  existing  streams,  with  which  in  some  cases  they  have  no 
obvious  connection.  In  the  valley  of  the  Medway,  for  instance, 
beds  of  gravel  may  be  found  at  various  stages  up  to  a  height  of 
about  300  feet  above  the  river.  They  indicate  that  the  Medway 
formerly  ran  in  the  same  general  direction  as  at  present,  that 
its  channel  then  was,  perhaps,  a  hundred  yards  above  that  in 
which  it  now  flows,  and  down  to  which.it  has  gradually  cut  its  way. 
But  in  order  that  the  bed  of  the  Medway  could  lie  at  the  higher 
level  the  whole  of  the  upper  part  of  its  basin  must  be  correspond- 
ingly raised ;  in  other  words,  all  the  land  which  it  drained  must 
have  been  well  above  the  3OO-feet  contour  line.  A  large  part  of  this 
area  is  now  200  or  even  250  feet  below  the  level  of  the  highest 
gravel ;  in  other  words,  a  valley  "  250  feet  deep  and  7  miles  broad" 
has  been  cut  out  since  that  epoch  by  rain  and  rivers.f  This  con- 
clusion once  attained,  there  is  comparatively  little  difficulty  in  under- 
standing how  the  Weald  as  a  whole  has  been  excavated  by  like  pro- 
cesses of  denudation;  and  the  more  the  face  of  the  earth  is  studied, 
by  passing  from  the  lowlands  to  the  highlands,  from  the  plains  to 
the  plateaus,  from  the  valleys  to  the  mountains,  the  more  strong 
becomes  the  conviction  that  rain  and  rivers  are  the  most  potent 
carving  tools  in  the  workshop  of  Nature. 

*  The  severance  of  the  eastern  end  from  the  main  mass  by  the  formation  of  the  English 
Channel,  as  will  be  explained  in  a  later  chapter,  is  an  event  of  comparatively  late  date. 

f  The  history  of  the  denudation  of  the  Weald  has  been  lucidly  described  by  Messrs. 
Foster  and  Topley  in  a  paper  in  the  Quarterly  Journal  of  the  Geological  Society,  vol.  xxi. 
(1865),  p.  443,  in  which  they  give  a  sketch  of  the  opinions  advocated  by  early  writers. 


CHAPTER  III. 

RIVERS   AS   TRANSPORTERS. 

WHEN  the  walls  of  Jerusalem  rose  again  from  ruin  in  the  days  of 
Nehemiah  every  man  in  the  one  hand  held  a  weapon,  with  the 
other  wrought  in  the  work.  So  it  is  with  all  the  forces  of  Nature — 
destruction,  transference,  rebuilding,  form  parts  of  a  continuous 
process.  Running  water  furrows  the  slope,  it  gashes  the  precipice, 
it  shapes  the  crag,  it  excavates  the  valley.  Not  content  with  the 
work  done  upon  the  surface,  it  even  mines  and  tunnels  under- 
ground. But  not  a  particle  is  removed  by  a  stream  from  any  part 
of  its  course  which  is  not  either  actually  transferred  to  a  new  posi- 
tion or  at  least  held  in  trust — invisible,  but  available,  like  money  on 
call  at  a  bank — until  it  is  required  for  use. 

So  the  transporting  action  of  moving  water  is  hardly  separable 
in  thought  from  its  destructive  action ;  and  the  former,  like  the  lat- 
ter, operates  both  chemically  and  mechanically.  These  effects 
also,  as  in  the  preceding  case,  are  not  easily  divided,  but  it  is  con- 
venient to  consider  them,  as  far  as  possible,  apart.  If  the  chemical 
effects  be  discussed  first,  as  in  the  last  chapter,  they  are  indicated 
by  springs,  especially  by  those  called  mineral.  When  water  flows 
out  of  the  earth  either  it  must  be  supplied  from  some  subterranean 
laboratory,  where  oxygen  and  hydrogen  have  been  compelled  to 
combine,  or  it  must  have  percolated  through  the  rock  from  the  sur- 
face; that  is  to  say,  directly  or  indirectly  it  must  be  traced  back  to 
the  rain.  The  former  source  is  an  improbable  one;  so  it  maybe 
assumed  that  the  water  has  fallen  from  the  sky,  has  gravitated 
downward  until  checked  by  some  impervious  bed,  has  made  its  way 
along  the  surface  of  this,  and  has  at  last  emerged  at  a  level  below 
that  at  which  its  journey  commenced.  If  the  water  be  traveling 
by  percolation,  it  slowly  trickles  forth ;  if  gathered  into  subter- 
ranean channels,  it  may  gush  out  with  considerable  strength. 

Rain  water,  as  already  said,  is  practically  free  from  mineral  salts, 
but  in  spring  water  these  are  always  present ;  sometimes,  it  is  true, 
in  very  minute  quantities,  but  often  enough  to  give  it  a  marked 
character.  Here,  as  at  Harrogate,  it  seems  to  be  seasoned  with 


KIVEKS  AS    TRANSPORTERS.  117 

rotten  eggs;  there,  as  at  Stachelberg,  it  is  yellow  and  stinks  of 
brimstone;  in  many  places,  as  at  Bath,  it  has  a  "flavor  of  warm  flat- 
irons,"  and  leaves  a  universal  trace  of  rust ;  in  others,  as  at  Droit- 
wich,  it  is  salt  as  brine.*  Around  the  geysers  of  Iceland  and  of 
the  Yellowstone  district  mounds  of  opaline  silica  are  raised  which 


FIG.  45. — GEYSER  AND  MOUND  OF  SILICA. 

imitate  the  craters  of  volcanoes  (Fig.  45) ;  the  white  and  pink  ter- 
races of  Rotomahana,  now  counted  among  the  world's  lost  wonders, 

*  The  result  of  pumping  brine  (which  is  formed  by  the  solution  of  beds  of  rock  salt  in 
the  percolating  underground  water)  at  Droitwich  is  thus  described  :  "  As  we  pass  through 
the  town  by  the  Birmingham  and  Bristol  line  of  the  Midland  Railway  a  strange  scene  of 
dilapidation  lies  before  us.  Every  chimney  is  out  of  the  perpendicular  ;  houses  appear  to 
be  sinking  in,  and  signs  of  active  subsidence  show  themselves  on  every  side  ;  the  very 
ground  over  which  the  line  passes  seems  hardly  safe  from  a  sudden  collapse  "  (C.  Parkin- 
son, Quarterly  Journal  of  the  Geological  Society,  1884,  p.  248).  The  effects  at  Northwich, 
in  Cheshire,  are  even  more  disastrous.  The  brine  at  Droitwich  and  at  Stoke  contains  from 
38  to  40  per  cent,  of  solid  matter,  42  being  the  saturation  point  of  common  salt. 


Il8  THE   STORY  OF  OUR  PLANET. 

were  built  up  by  similar  deposits  from  the  hot  springs  of  New 
Zealand  (Fig.  46).  Chlorides,  sulphates,  and  nitrates  of  soda  and 
potash,  salts  of  iron  and  of  lime,  are  among  the  more  frequent 
products  of  mineral  springs,  all  of  which  are  obtained  from  or 
found  among  the  constituents  of  the  earth's  crust,  and  can  be  sepa- 
rated from  "it  by  water,  especially  if  this  be  slightly  acidulated,  as  it 
is  generally,  as  a  result  of  the  decomposition  of  organisms. 

The  mineral  character  of  the  rocks  which  have  been  traversed 
mainly  determines  the  nature  and  quantity  of  the  salts.  In  lime- 
stone districts  the  water  of  wells  and  springs,  as  every  housewife 
knows,  is  hard — that  is  to  say,  contains  a  considerable  quantity  of 
bicarbonate  of  lime.  This  compound,  which  consists  of  two  mole- 
cules of  carbonic  acid  in  combination  with  one  molecule  of  lime,  is 
soluble  in  water,  but  not  so  the  carbonate — just  as  a  weight  might 
be  floated  by  two  bladders  which  would  sink  with  one.  The  bicar- 
bonate is  an  unstable  compound,  or,  to  carry  on  the  simile,  one  of 
the  bladders  is  attached  by  a  thin  string  which  is  easily  broken.  So 
when  the  water  evaporates,  either  from  heat  or  from  exposure  to 
the  air,  one  molecule  of  carbonic  acid  is  detached  and  the  carbonate 
of  lime  is  precipitated.  Thus  pipes,  kettles,  and  boilers  are 
"furred";  the  roofs  of  caverns  are  hung  with  stalactites,  or  stony 
icicles;  their  floors  are  covered  with  stalagmite,  a  natural  pavement 
formed  and  laid  down  by  the  drip  from  above ;  below  the  mouths 
of  springs  great  banks  of  limestone,  called  tufa  or  travertine,  are 
slowly  deposited.  These  may  be  seen,  to  take  one  example  out  of 
many,  in  the  valley  of  the  Derwent,  at  Matlock,  below  the  "petrify- 
ing wells,"  where  eggs,  birds'  nests,  and  sundry  objects  are 
incrusted,  and  find  sale  among  visitors  who  have  a  liking  for  curiosi- 
ties; but  at  some  places,  such  as  Clermont  Ferrand  or  St.  Nectaire 
in  Auvergne,  more  artistic  results  are  obtained,  for  the  water  is 
made  to  flow  very  gently  over  a  number  of  molds,  and  the  carbon- 
ate of  lime  thus  deposited  makes  very  pretty  casts.  At  the  former 
place  a  small  natural  bridge  has  been  built  across  a  stream  by  the 
deposit  from  the  water  which  runs  away  after  it  has  been  utilized 
at  the  factory.  Huge  banks  of  tufa  are  formed,  according  to 
Tchihatchef,  by  the  deposit  from  the  hot  springs  near  the  ancient 
Ionian  city  of  Hierapolis;  this  also  has  spanned  a  little  valley  with 
a  bridge,  quaint  but  picturesque.* 

Rivers  also  testify  to  the  solvent  power  of  water.     As  they  are 

*  A  figure  of  this  is  given  by  Reclus,  "  The  Earth,"  ch.  xli. 


120  THE   STORY  OF  OUR  PLANET. 

partly  fed  by  springs,  this  is  to  be  expected,  but  the  quantity  of 
mineral  matter  held  in  solution  is  often  too  great  to  be  explained 
only  in  this  way.  It  must  also  have  been  obtained  by  the  streams 
as  they  were  excavating  their  sub-aerial  channels  and  wearing  rock- 
fragments  into  pebbles,  sand,  and  mud.  It  will  be  enough  to  quote 
three  analyses  of  river  water,  out  of  the  many  which  have  been  pub- 
lished, to  show  how  large  a  quantity  of  mineral  salts,  comparatively 
speaking,  is  carried  in  solution,  and  how  much  this  depends  upon 
the  character  of  the  rocks  in  different  districts.  In  the  water  of  the 
Scotch  Dee,  near  Aberdeen,  the  solid  matter  in  solution  amounts 
to  3.12  parts  by  weight  in  a  hundred  thousand,  of  which  1.22  con- 
sist of  carbonate  of  lime.  The  proportion  in  the  water  of  the 
Rhine,  above  Bale,  is  17.12,  of  which  12.79  are  carbonate  of  lime 
and  1.54  sulphate  of  lime.  But  in  the  Thames,  near  Ditton,  the 
proportion  is  27.20,  of  which  16.84  are  carbonate  of  lime  and  4.37 
are  sulphate.  Thus  in  these  three  rivers  the  amounts  of  carbonate 
of  lime  alone  are  as  the  numbers  122,  1279,  and  1684,  or,  as  a  rough 
estimate,  the  Thames  transports  in  solution  a  third  as  much  again 
of  this  mineral  as  the  Rhine,  and  fourteen  times  as  much  as  the 
Dee.  This  disproportion  is  readily  understood  on  investigating  the 
geology  of  the  areas  drained  by  these  three  rivers.  In  the  basin  of 
the  Dee  the  rocks  are  but  rarely  calcareous,  and  consist  almost 
exclusively  of  silicates,  which  are  with  difficulty  soluble  in  water. 
The  Rhine  and  its  Alpine  tributaries  flow  partly  over  similar  rocks, 
partly  over  limestones;  these,  however,  occupy  a  much  larger  share 
proportionately  of  the  drainage  area  of  the  Thames. 

The  immense  quantity  of  material  thus  transported,  by  a  river 
which  counts  as  a  small  one  among  those  of  the  world,  may  be  more 
readily  appreciated  by  another  mode  of  representation.  It  has 
been  estimated  that  the  Thames,  as  it  flows  under  Kingston  Bridge, 
carries  in  solution,  on  an  average,  about  1514  tons  of  mineral  salts 
in  the  course  of  twenty-four  hours.  Of  this  about  1000  tons  is  car- 
bonate of  lime.  A  ton  of  chalk  is  a  mass  measuring  about  15 
cubic  feet,  so  that  15,00x3  cubic  feet  of  chalk — in  other  words,  a 
block  10  feet  square  and  150  feet  long — slips  invisibly  past  King- 
ston; enough,  in  the  course  of  a  year,  to  cover  the  whole  area  of 
Westminster  Abbey  with  a  solid  mass  of  limestone  nearly  9  feet 
high. 

But  not  in  this  form  only  is  matter  transported.  The  bed  of 
every  torrent  is  strewn  with  bowlders  and  gravel,  that  of  a  quieter 
stream  with  sand  and  mud.  By  listening  at  the  side  of  a  swollen 


RIVERS  AS   TRANSPORTERS. 


121 


Alpine  torrent  we  can  hear  the  bigger  stones  groaning  and  thud- 
ding as  they  are  rolled  along;  we  can  see  the  water  in  every  stream 
at  flood  time  thick  with  suspended  silt.  If  a  river  flows  at  the  rate 


Large  boiling  water 
basins  or  Geysers 
0     Smaller  hot  springs 

Fumaroles  GfSolfatat-a 
»     Mud  Volcanoes 


&JBoutall  sc, 

FIG.  47. — MAP  OF  VOLCANIC  DISTRICT,  ROTOMAHANA. 

of  300  yards  an  hour,  it  can  just  wear  away  and  move  along  soft 
clay ;  with  double  that  speed  fine  sand  is  transferred ;  as  the 
velocity  increases  so,  rapidly,  does  the  size  of  the  materials,  and 
when  it  attains  to  a  pace  of  4800  yards,  or  about  2^  miles  an  hour, 
pebbles  an  inch  and  a  half  in  diameter  are  swept  along.  The  first 
rate  is  that  of  slow-flowing  rivers,  such  as  those  in  the  fenlands  of 
Holland  or  of  Eastern  England ;  the  last  more  nearly  represents 


122    •  THE   STORY  OF  OUR  PLANET. 

that  of  the  great  European  rivers,  such  as  the  Rhine  at  Bale,  or  the 
Danube  at  Vienna.*  A  considerable  quantity  of  finer  detritus,  as 
said  above,  is  also  carried  by  the  quicker  streams  at  all  times,  by 
the  slower  during  a  flood.  This  moves  in  a  state  of  suspension  in 
the  waters,  like  dust  in  the  air,  the  coarser  stuff  being  swept  by  the 
stream,  as  by  a  besom,  along  its  bed.  It  has  been  estimated  that 
the  Rhine,  even  when  its  waters  are  low,  transports  sediment  to  the 
amount  of  I  part  in  7000  by  weight;  but  the  proportion  rises  to  I 
in  2000  under  ordinary  circumstances,  and  reaches  I  in  230  at  flood 
time.  The  Ganges  and  Brahmapootra  are  said  to  discharge  annu- 
ally into  the  Bay  of  Bengal  about  40,000,000,000  cubic  feet  of  sedi- 
ment. This,  at  a  rough  estimate,  might  be  piled  up  in  a  pyramidal 
hill  measuring  4  miles  along  each  side  and  in  height  300  feet.  The 
Ganges  alone  is  believed  to  bring  down  sufficient  mud  to  cover  172 
square  miles  with  a  layer  I  foot  thick.  Suppose  this  material  formed 
into  a  similar  hill,  with  its  base  covering  a  square  mile,  this  would 
be  516  feet  high.  But  the  Ganges  is  beaten  by  the  Mississippi,  for 
its  pyramid  would  rise  to  804  feet;  while  the  Hoangho  works  yet 
harder  to  fill  up  the  Yellow  Sea,  for  the  pyramid  formed  of  its 
detritus  would  tower  up  to  2190  feet. 

Some  of  the  materials  thus  transported  by  a  river  are  not  carried 
very  far.  No  sooner  is  its  velocity  checked  than  the  coarser  stuff 
is  deposited.  Shoals  form  in  rivers  in  the  stiller  waterat  the  junc- 
tion of  cross  currents  and  against  the  convexities  of  the  banks.  If 
a  narrow  strip  of  level  ground  chance  to  occur  by  the  side  of  a  tor- 
rent in  an  Alpine  glen,  this  is  a  stony  waste  of  bowlders,  which 
have  been  dropped  there  in  times  of  flood.  Where  the  glen  enters 
a  main  valley,  and  its  waters  are  discharged  into  the  latter  from  a 
slightly  higher  level,  as  happens  at  many  places  in  the  valley  of  the 
Rhone,  between  Martigny  and  Brieg,  the  bowlders  and  gravel, 
mixed  with  sand,  which  have  been  successfully  swept  down  the 
steeper  inclines,  are  at  once  piled  up  in  a  "cone  of  dejection"  or  an 
"alluvial  fan."  These  sloping  mounds  of  ddbris  before  the  entrances 
of  lateral  glens  are  common  features  in  the  scenery  of  a  mountain 
region  like  Switzerland.  T  icy  may  be  readily  recognized  in  that 
beautiful  view  of  the  Rhone  valley  which  is  obtained  on  the  descent 
from  the  Baths  of  Leuk  to  the  village  of  the  same  name.  In  the 
Rocky  Mountains,  the  Himalayas,  and  other  great  chains  these 

*  This  would  he  the  maximum  velocity.  In  a  fairly  rapid  river  the  minimum  velocity  is 
to  the  maximum,  roughly,  in  the  proportion  of  3  :  5  ;  in  a  slow  one  as  i  :  2. 


RIVERS  AS   TRANSPORTERS.  123 

"fans"  are  many  miles  in  diameter  and  hundreds  of  feet  in  thick- 
ness. But,  besides  this,  the  beds  of  the  larger  mountain  valleys  are 
being  continually  raised  by  the  debris  which  is  deposited  in  them 
during  floods.  At  such  times  much  of  the  coarser  material  does 
not  rest  upon  the  cone,  but  is  hurried  on  and  spread  out  over  the 
level  floor  of  the  main  valley.*  The  plateau  of  La  Batie  between 
the  Rhone  and  the  Arve,  below  Geneva,  is  a  thick  mass  of  gravel; 
from  its  pleasant  walks  the  opposite  cliff  overhanging  the  former 
river  is  seen  to  be  wholly  composed  of  irregularly  stratified  beds  of 
sand  and  pebbles,  which  have  been  brought  down  by  the  Arve  from 
the  mountains  of  Savoy.  The  lowlands,  for  miles  around  Bale, 
consist  of  similar  pebble  beds,  the  deposits  of  the  Rhine  and  its 
tributaries  comparatively  late  in  their  geological  history.  The 
plains  of  Piedmont  and  Lombardy  are  one  widespread  mass  of 
gravel,  the  dtbris  of  that  vast  mountain  wall  which  sweeps  around 
the  whole  basin  of  the  Po. 

A  delta  is  only  another,  and  a  yet  more  complete,  proof  of  the 
transporting  power  of  running  water.  When  a  river  enters  a  lake 
or  falls  into  the  sea,  the  velocity  of  it's  current  is  at  once  checked, 
and  the  deposit  of  detritus  is  correspondingly  rapid.  In  the  Alpine 
lakes  the  muddy  and  the  clear  water  are  sometimes  very  sharply 
separated,  the  one  being  suspended  in  the  other,  like  a  cumulus 
cloud  in  the  blue  sky.  This  can  be  watched  as  it  rolls  obliquely 
downward  into  the  clearer  depths,  in  the  same  way  as  smoke  drifts 
upward  into  the  air.  Sometimes  the  division  between  the  two  is 
so  sharp  that  the  bow  of  a  boat  may  be  in  clean  and  the  stern  in 
turbid  water.  But,  in  any  case,  on  looking  down  upon  the  embou- 
chure of  a  river  from  one  of  the  hills  above  an  Alpine  lake  an  area 
of  discolored  water  can  be  at  once  detected — in  outline  a  rude 
triangle  or  parabola,  the  apex  pointing  away  from  the  shore.  The 
mud  sinks  slowly  to  the  bottom,  drifting  along  with  the  gently 
moving  water,  so  that  the  materials  must  be  to  some  extent  sorted. 
Much  of  it  descends  at  rates  varying  from  ten  to  four  feet  an  hour, 
but  the  finest  particles  settle  down  still  more  slowly,  and  may  be 
many  months  in  reaching  the  bottom,  if,  indeed,  they  ever  come  to 
rest.  The  turquoise  tint  of  the  water  in  many  lakes  is  due  to 
these,  and  even  the  exquisite  blue  of  the  Rhone  as  it  issues  from 
the  Lake  of  Geneva  is  attributed  to  the  presence  of  suspended  par- 

*  The  effect  of  floods  is  often  checked  by  banking  in  the  stream,  but  this,  of  course,  only 
alters  the  form  of  the  area  over  which  the  debris  is  deposited,  and  produces  other  conse- 
quences, which  will  be  presently  described. 


124  THE   STORY  OF  OUR  PLANET. 

tides  of  almost  inconceivable  minuteness.  The  water  beneath  the 
walls  of  Chillon  has  a  different  tint  from  that  which  flows  by  Rous- 
seau's Island;  the  water  of  the  Lake  of  Brienz  is  more  distinctly 
green  than  that  of  the  Lake  of  Thun,  because  the  Aar  empties 
itself  directly  into  the  one  and  only  the  Lutschine  into  the  other. 

At  the  Rivington  waterworks,  which  supply  Liverpool,  a  delta 
estimated  as  containing  6306  cubic  yards  was  formed  in  one  of 
the  reservoirs  in  twenty-seven  years  by  the  stream  from  a  gathering 
ground  not  quite  one  square  mile  and  a  fifth  in  area,  on  which  the 
average  rainfall  was  49/^  inches.*  In  the  same  period  the  Reuss 
had  deposited  in  the  Lake  of  Lucernef  a  delta  estimated  to  contain 
more  than  141,000,000  of  cubic  feet,  which  would  be  equivalent  to 
a  daily  deposit  of  19,350  cubic  feet,  or  a  solid  block  50  feet  long,  43 
wide,  and  9  high.  The  lakes  of  Thun  and  Brienz  formerly  must 
have  been  one  sheet  of  water.  They  have  been  divided  by  the 
detritus  brought  down  on  the  one  side  by  the  Lutschine  from  the 
glaciers  of  the  Oberland,  on  the  other  by  the  Lombach  from  the 
lower  summits  of  the  Habkerenthal.  The  openings  of  the  valleys 
are  about  a  couple  of  miles  apart,  so  the  delta  of  the  Lutschine  first 
forces  the  Aar  to  graze  the  base  of  the  Harder  at  Interlaken ;  then 
the  river  is  driven  over  to  the  southern  side,  as  it  comes  within  the 
influence  of  the  delta  of  the  Lombach.  Yet  the  depth  of  the  basin 
in  this  part  must  have  been  originally  between  seven  and  eight 
hundred  feet.  The  level  plains  which  extend  for  some  miles  up 
the  valleys  above  the  heads  of  the  Alpine  lakes  are  all  deltas  which 
have  been  formed  by  the  detritus  brought  down  by  the  rivers.  To 
take  a  single  case  as  an  example  of  many:  Once  upon  a  time  the 
Lake  of  Geneva  must  have  extended  up  to  St.  Maurice,  where  a 
rocky  barrier  forms  the  portal  of  Canton  Valais.  From  that  spot 
to  Bouveret  on  the  present  shore  is  a  distance  of  about  fourteen 
miles.  From  the  margin  of  the  land  the  water  at  first  deepens  very 
slowly,  the  face  of  the  mass  of  debris  shelving  gently  down  to  a 
depth  of  nearly  a  thousand  feet.  Its  total  length  may  be  estimated 
at  about  ten  miles.  But  immediately  opposite  to  the  actual 
embouchure  the  current  of  the  river  has  still  sufficient  influence  to 
interfere  partially  with  the  deposit  of  debris,  so  that  down  to  a  depth 
of  about  eight  hundred  feet  a  deep  inlet  is  formed  in  all  the  contour 
lines.  Egypt,  to  quote  the  old  saying,  is  "the  gift  of  the  Nile," 
and  the  same  is  true  in  other  parts  of  the  world.  The  deltas 

*  T.  M.  Reade,  Quarterly  Journal  of  the  Geological  Society,  1884,  p.  263. 
f  A  rectification  of  the  course  of  the  river  had  been  made. 


RIVERS  AS    TRANSPORTERS.  125 

formed  when  rivers  fall  into  the  sea  are  proofs  of  their  transporting 
power,  but  on  a  much  grander  scale  than  in  the  case  of  lakes. 
Here,  however,  a  new  influence  is  brought  to  bear,  that  of  the  tide, 
so  the  description  of  such  deltas  as  these  is  better  postponed  to  a 
later  chapter. 

The  general  effect  of  floods  has  been  already  mentioned,  but  one 
or  two  particular  cases  demand  a  brief  notice.  As  the  nature  of 
some  people  is  wholly  changed  in  a  fit  of  passion,  so  the  character 
of  a  stream  may  be  completely  altered  in  a  time  of  flood.  The  rill 
may  become  a  river,  the  purling  brook  a  roaring  torrent.  This  of 
course  will  only  happen  after  an  exceptionally  heavy  fall  of  rain, 
but  such  an  event  now  and  again  occurs  in  regions  where,  as  a  rule, 
eccentricities  of  climate  are  rare.  On  the  night  of  August  2,  1879, 
full  four  inches  of  rain  fell  at  Cambridge  between  about  eight 
o'clock  in  the  evening  and  four  o'clock  in  the  morning.  By  nine 
o'clock  a  little  brook  which  drains  a  shallow  valley  some  four  miles 
long,  and  usually  creeps  at  a  snail's  pace  through  the  grounds  of 
St.  John's  College  to  the  Cam,  had  become  a  swift  stream,  and  had 
laid  under  water  much  land  on  either  side  of  its  banks.  In  two  or 
three  hours  more,  when  the  Cam  became  similarly  swollen,  all  the 
lower  ground  in  the  valley  was  flooded,  and  the  water  came  up  to 
within  about  a  couple  of  feet  of  the  crown  of  the  arches  at  one  of 
the  bridges. 

But  the  floods  in  a  lowland  region,  though  sometimes  mis- 
chievous and  making  a  great  mess  with  the  mud  and  gravel  which 
they  are  apt  to  distribute  over  cultivated  land,  are  comparatively 
unimportant.  In  rivers  which  issue  from  mountain  masses,  espe- 
cially where  the  slopes  are  steep  and  the  valleys  contracted,  the 
stream  in  a  narrow  part  of  its  channel  may  rise  forty  or  fifty  feet, 
and  cover  many  a  square  mile  where  it  debouches  on  the  lowland. 
The  floods  of  the  Garonne  are  often  exceptionally  disastrous.  In 
the  year  1875  one  rose,  even  at  Toulouse,  to  a  height  of  some  thirty 
feet,  and  swept  away  two  suspension  bridges.  Frequently,  as  we 
traveled  over  the  country,  broken  bridges  were  seen.  Sometimes 
a  pier  was  so  completely  destroyed  that  only  a  break  in  the  sur- 
face of  the  stream  indicated  its  place. 

Occasionally  a  flood  is  so  much  localized  as  to  call  for  a  special 
notice,  since  the  result  is  rather  exceptional.  In  the  month  of  July, 
1887,  part  of  the  level  bed  of  the  Ziller-thal,  in  the  Tyrol,  presented 
a  melancholy  spectacle.  A  mass  of  debris,  consisting  of  black  mud 
mingled  with  blocks  of  rock  sometimes  several  cubic  feet  in  volume, 


126  THE   STORY  OF  OUR  PLANET. 

had  swept  across  from  the  foot  of  the  mountains,  burying  cornfields 
and  meadows,  brushwood  and  gardens.  Through  this  scene  of  ruin 
a  little  stream,  only  a  few  inches  deep  and  perhaps  a  couple  of 
yards  wide,  ran  rippling  toward  the  river.  Yet  this  seemingly  harm- 
less rill  had  wrought  that  devastation,  destroying  two  houses,  and 
utterly  ruining  many  acres  of  good  meadow  land.  Its  course  down 
the  mountain  slopes  is  comparatively  short,  but  the  rocks  through 
which  it  has  furrowed  a  channel  are  friable,  and  easily  swept  away. 
Exactly  over  this  place  a  violent  storm  had  burst;  just  for  an  hour 
the  stream  had  become  a  raging  torrent,  a  foaming  mass  of  black 
mud  and  rock  fragments,  and  this  was  the  result.  The  rubbish  lay 
two  or  three  feet  deep  in  the  open  part  of  the  valley,  some  hun- 
dreds of  yards  from  the  slopes,  and  the  bowlders  not  seldom  were 
three  or  four  feet  in  diameter. 

Sometimes,  under  very  exceptional  circumstances,  a  flood  may  be 
even  less  liquid  than  the  last  described,  and  a  mass  of  mud  emerges 
from  some  mountain  recess,  like  a  glacier  of  exceptional  filth  and 
softness.  Such  an  one  in  the  year  1835  descended  from  the  Dent 
du  Midi  to  near  Evionnaz,  in  the  valley  of  the  Rhone.  The  coarse 
thick  mud,  mixed  with  bowlders,  slowly  crept  down  from  the  moun- 
tain side,  sweeping  through  a  pine  forest  "as  if  it  were  straw  in  a 
stubble  field,"  destroying  houses  and  burying  cultivated  tracts.  The 
high-road  was  covered  for  about  a  furlong,  and  to  a  depth,  in  places, 
of  several  feet. 

Landslips  also  may  be  counted  among  the  effects  of  water, 
though  here  its  action  is  mainly  indirect,  for  it  does  little  more  than 
initiate  the  catastrophe,  and  the  transport  of  material  is  due  to 
gravitation.  The  conditions  fora  landslip  are  the  following:  At 
the  top  must  be  a  thick  mass  of  rock,  through  which,  though  fairly 
strong  and  hard,  water  can  make  its  way;  beneath  this  a  bed  rather 
less  coherent  in  nature;  and  below  that  a  third,  which  is  impervious 
to  water.  These  rocks  also  must  be  disposed  so  as  to  slope  slightly 
outward  to  the  face  of  a  cliff  or  of  a  steep  hillside.  After  a  rainy 
season  the  middle  seam  becomes  saturated  with  water,  and  its 
materials  are  rendered  less  coherent.  It  yields  to  the  pressure  of 
the  overlying  mass,  which  at  last  begins  to  glide  downward,  like  a 
building  of  which  the  foundations  have  been  sapped.  When  once 
it  has  broken  loose  from  a  hillside,  the  mass,  like  the  stone  of 
Sisyphus,  "thunders  impetuous  down  and  smokes  along  the 
ground."  Landslips  on  a  small  scale  are  not  rare  on  some  parts  of 
the  English  coast.  Thus  has  been  formed  the  beautiful  Undercliff 


RIVERS  AS   TRANSPORTERS.  127 

in  the  Isle  of  Wight.  The  chalk  and  the  cherty  beds  of  the  Upper 
Greensand  rest  upon  less  coherent  materials,  and  these  are  sup- 
ported by  the  impervious  blue  clay  called  the  Gault,  all  the  beds 
sloping  toward  the  sea.  From  time  to  time  great  masses  have 
slipped  forward  from  the  face  of  the  range  of  hills  which  culminates 
in  St.  Catherine's  Point,  plowing  up  the  clay,  and  breaking  up  as 
they  descended  into  smaller  fragments;  so  that  the  whole  presents 
a  scene,  geologically  speaking,  of  the  wildest  confusion.  Similar 
slips  occur  frequently  on  the  Dorset  coast,  west  of  Swanage,  but 
the  most  noted  is  to  be  found  between  Lyme  Regis  and  Axmouth. 
Here  the  cliffs  rise  to  a  height  of  full  a  hundred  feet,  and  the 
general  arrangement  of  the  strata  resembles  that  in  the  Isle  of 
Wight.  Small  landslips  are  common,  but  the  greatest  on  record 
occurred  on  December  24,  1839,  after  an  unusually  wet  season. 
Then  a  deep  chasm,  nearly  three-quarters  of  a  mile  in  length,  almost 
instantaneously  opened  out  in  the  fields  at  the  top  of  the  cliff, 
parallel  with  the  shore,  and  the  intervening  strip  of  land,  sometimes 
a  hundred  yards  wide,  slipped  forward  toward  the  sea,  breaking  up 
as  it  went  into  a  number  of  large  fragments.* 

In  mountain  districts  these  landslips  are  yet  more  formidable, 
and  have  frequently  wrought  much  destruction  to  life  and  property. 
Hundreds  of  acres  of  fertile  lands  may  be  buried  deep  beneath  a 
wild  waste  of  broken  rock  and  tumbled  crags.  One  instance  may 
serve  as  an  example  of  many;  and  no  better  could  be  found  than 
the  noted  case  of  the  fall  of  the  Rossberg,  the  ruins  of  which  are 
now  crossed  by  everyone  who  travels  along  the  St.  Gothard  rail- 
way from  Lucerne  toward  the  valley  of  the  Reuss.  The  thick  bed 
of  hard  pudding  stone  which  forms  the  upper  part  of  the  Rossberg, 
as  well  as  of  the  better  known  Rigi,  rests,  as  described  above,  upon 
a  less  coherent  mass,  from  which  the  water  cannot  readily  escape. 
On  the  morning  of  September  27,  1806,  at  the  end  of  a  very  wet 
period,  which  had  lasted  for  several  months,  a  large  mass  of  the 
pudding  stone,  after  some  brief  preliminary  warnings,  suddenly 
broke  loose  and  fell,  shattered  into  fragments,  on  the  devoted 
valley.  Huge  blocks  of  stone  were  hurled  through  the  air,  reach- 
ing across  the  flat  meadows  to  the  lower  slopes  of  the  Rigi,  and  in 
a  few  minutes  a  large  tract  of  populous  and  fruitful  country  was 

*  After  the  above  paragraph  was  written  another  instance  was  added  to  the  list  by  the 
landslip  at  Sandgate  on  March  4  and  5,  1893.  This,  however,  was  rendered  noteworthy, 
not  so  much  for  the  magnitude  of  the  mass  displaced  as  for  the  destruction  of  property, 
since  part  of  the  town  was  built  on  the  ground  which  slipped. 


128  THE   STORY  OF  OUR  PLANET. 

hidden  beneath  a  mass  of  ruin.  The  village  of  Goldau  and  three 
neighboring  hamlets  were  covered  with  confused  piles  of  rock  and 
earth  from  100  to  200  feet  in  thickness,  under  which  they  still 
remain  buried.  Of  the  inhabitants  433  lost  their  lives,  as  well  as  24 
strangers.  According  to  a  rough  estimate,  the  portion  of  the 
mountain  that  fell  measured  a  league  in  length,  a  thousand  feet  in 
breadth,  and  a  hundred  feet  in  thickness.* 

In  these  cases,  however,  the  transporting  effects  of  water,  though 
locally  important,  are  limited  in  extent.  Here,  as  elsewhere,  the 
rule  is  observed,  which  holds  generally  in  Nature,  that  the  intensity 
of  the  disturbing  action,  and  the  area  affected  by  it,  are  roughly  in 
inverse  proportions.  The  surface  of  the  earth  is  modified  by  the 
ordinary  action  of  rain  and  rivers  far  more  than  by  the  exceptional 
fury  of  deluges.  It  loses  and  it  gains  by  the  almost  silent  and 
imperceptible  transfer  of  material  through  the  water  which  streams 
from  every  slope  and  flows  away  in  silent  strength  from  every 
mountain  system,  which  glides  through  the  lowlands  and  finds  at 
last  its  bourne  in  the  sea,  far  more  than  it  does  by  the  rush  of  mud 
avalanches  or  by  the  rage  of  cataclysms. 

*  Ball,  "  Alpine  Guide,  Central  Alps,"  §  26  C. 


CHAPTER  IV. 

ICE  AS   SCULPTOR. 

WATER  is  converted  into  ice  when  its  temperature  falls  below 
32°  F.  As  the  fluid  becomes  a  solid,  its  volume  increases  largely 
and  suddenly,  1000  cubic  inches  of  water  making  1102  cubic  inches 
of  ice.  The  force  possessed  by  the  expanding  mass  is  very  great. 
This  has  been  strikingly  illustrated  by  an  experiment  made  many 
years  since  in  Canada,  which  has  been  often  repeated,  under  slightly 
different  conditions,  in  laboratories.  A  bombshell  of  the  old 
pattern,  about  13  inches  in  diameter  and  an  inch  in  thickness, 
was  filled  with  water,  and  the  touch  hole  tightly  corked  by  a 
plug  weighing  3  pounds.  The  shell,  with  its  contents,  was  then 
exposed  to  the  severe  cold  of  a  winter  night.  In  a  short  time  the 
plug  was  projected  to  a  distance  of  415  feet,  and  a  tongue  of  ice,  as 
it  were  in  derision,  was  protruded  from  the  orifice.  The  experi- 
ment was  repeated,  but  this  time  the  plug  was  too  tightly  fixed  to 
be  ejected,  so  the  shell  itself  was  split. 

The  bursting  of  water  pipes  in  houses,  so  common  in  a  severe 
frost,  supplies  the  tenant  with  an  object  lesson,  the  plumber  with 
work,  and  the  cynic  with  another  characteristic  example  of  British 
unwisdom,  which  cannot  be  taught  to  provide  for  any  but  the  most 
ordinary  contingencies.  Similar  object  lessons  are  yet  commoner 
outside  than  they  are  inside  the  houses.  After  a  hard  frost  which 
has  followed  on  damp  weather  the  pointing  drops  out  of  the  joints 
of  walls,  and  the  bricks,  especially  in  the  jerry-built  structures 
of  the  nineteenth  century,  crack  and  crumble  away.  Even  the  sur- 
faces of  rocks  scale  off  in  flakes,  sometimes  several  pdunds  in 
weight.  In  a  railway  cutting  through  any  rather  porous  rock  these 
flakes  may  be  often  seen  in  plenty  lying  in  the  gutter  at  the  foot 
of  the  walls.  Beneath  a  cliff  they  are  strewn  in  like  manner,  though 
here  their  history  is  less  readily  recognized  by  an  inexperienced 
eye.  Nevertheless,  the  talus,  or  sloping  bank  of  angular  fragments, 
which  is  usually  present  at  the  foot  of  a  cliff,  has  been  formed — at 
any  rate,  in  a  climate  like  that  of  England — mainly  by  the  expan- 
sive effect  of  water  in  freezing,  though  no  doubt  mere  alterations  of 


130  THE   STORY  OF  OUR  PLANET. 

temperature,  as  already  explained,  have  also  taken  part  in  the  work. 
The  flanks  and  summits  of  mountains  often  tell  the  same  tale.  The 
stone  avalanches  which  thunder  down  their  precipitous  slopes  are 
started  by  frost,  and  mainly  consist  of  blocks  detached  by  the 
action  of  ice.  In  some  places  the  discharge  during  the  day  is 
almost  incessant,  but  it  does  not  wholly  cease  at  night.  On  such 
a  peak  as  the  Matterhorn  the  sleeper  in  the  upper  hut  will  probably 
be  awakened  three  or  four  times  by  the  roar  of  the  stony  cataract 
down  the  eastern  face  of  the  mountain,  and  instinctively  presses 
closer  to  the  shelter  of  the  crag.  Rocky  and  lofty  summits  are  not 
seldom  natural  cairns:  blocks  poised,  not  always  too  securely,  one 
on  another,  so  that  it  is  not  easy  to  be  sure  where  the  live  rock 
begins.  In  Arctic  regions,  as  described  by  travelers,  the  rocks  are 
often  completely  shattered  by  the  frost.  The  crags  in  winter,  as 
it  were,  burst  asunder  with  a  loud  report ;  huge  masses  are  detached, 
which  sooner  or  later  tumble  down  upon  either  the  frozen  shore  or 
the  surface  of  the  ice.* 

But  frozen  water  does  not  only  play  the  part  of  a  wedge,  it  acts 
also  in  the  form  of  snow  and  glacier.  The  latter  is  more  local  in 
its  operations  than  the  former,  but  its  effects  are  the  more  dis- 
tinctly marked.  Snow  falls  when  the  temperature  of  a  considerable 
layer  of  moist  air  sinks  below  32°  F.  If  the  temperature  continues 
low,  the  snow  does  not  melt,  but  gradually  accumulates.  In  such 
a  case  it  is  commonly  ineffective  as  an  agent  of  denudation  ;  indeed, 
as  the  temperature  of  a  thick  layer  of  snow  does  not  readily  fall 
much  below  32°  F.,  such  a  layer  acts  like  a  cloak  in  protecting  the 
surface  of  the  earth  from  a  severe  frost.  But  in  one  case  disturb- 
ances may  be  produced.  In  Britain,  when  a  thaw  begins,  any  snow 
resting  upon  a  sloping  roof  is  apt  to  slip  and  scale  off  suddenly,  the 
event  being  announced  by  a  heavy  thud — sometimes  by  a  crash  of 
glass,  if  a  greenhouse  has  been  built  below  in  a  convenient  position. 
In  like  ivnnner  the  snow  slips  away  from  the  mountain  side  in  great 
masses,  called  avalanches.  These  sometimes  consist  of  powdery 
snow;  such  are  called  in  the  Alps  "dust  avalanches."  They  may 
happen  at  any  time  soon  after  a  heavy  fall  of  snow,  before  the  mass 
consolidates  and  unites  itself  with  the  surface  below.  Others  of 
greater  consistency  are  called  "ground  avalanches."  These  are 
formed  of  the  snow  which  has  lain  long  on  the  mountain  side,  and 


*  "  Nordenskiokl's  Arctic  Voyages,"  ch.  iv.;  H.  W.  Feilden,  Quarterly  Journal  of  the 
Geological  Society,  r878,  p.  564. 


ICE  AS  SCULPTOR.  131 

fall  when  the  spring  is  advancing  and  the  warmer  weather  is  begin- 
ning to  set  in.  They  are  on  a  larger  scale  than  the  others,  consist- 
ing of  thicker  and  more  solid  masses,  and  m  consequence  are  the 
more  destructive.  They  sweep  a  path  clean  through  the  smaller  or 
more  open  pine  woods,  snapping  the  boles  oft  short  or  uprooting 
the  trees;  they  tear  up  turf  and  bushes  and  stones  from  the  hill- 
side, and  either  strew  the  slopes  below  with  debris  or  hurl  it  into 
the  valley,  where  the  piled  up  snow  often  lingers  long  into  the 
summer  months,  and  sometimes  may  be  seen  completely  bridging 
the  torrent.  But  ice  is  more  potent  as  a  scuplturing  tool  in  the 
form  of  a  glacier.  In  brief  outline  the  history  of  "a  river  of  ice,"  as 
it  has  been  sometimes  called,  is  as  follows:  A  place  some  height 
above  the  sea  level,  as  already  said,  has  a  lower  mean  temperature 
than  one  by  the  water  side;  for  instance,  the  mean  annual  tempera- 
ture of  Fort  William,  on  the  west  coast  of  Scotland,  is  46.8°  F. ;  at 
the  observatory  on  the  summit  of  Ben  Nevis  it  is  30.9?  F.  This 
indicates  a  fall  of  i°  F.  for  each  277  feet  of  ascent,  which  is  rather 
exceptionally  rapid.  As  the  change  is  very  dependent  upon  local 
circumstances,  it  is  difficult  to  fix  upon  a  normal  rate  of  fall,  but 
about  I  °  F.  for  each  300  feet  of  ascent  is  probably  not  far  wrong.* 
Thus,  even  under  the  equator,  the  mean  temperature  of  the  upper 
part  of  a  great  mountain  is  below  32°  F.  The  lofty  volcanic  sum- 
mits of  the  Ecuadorian  Andes  are  thickly  clothed  with  perennial 
snow,  and  even  give  rise  to  occasional  glaciers.  The  isothermal  of 
32°  is  at  the  sea  level  some  little  distance  south  of  Fredrichshaab, 
near  the  southern  end  of  Greenland,  but  on  the  peak  at  Ben  Nevis 
it  is  at  an  elevation  of  about  4100  feet,  over  that  of  Snowdon  at 
about  5500.  In  the  Alps  the  position  of  the  isothermal  of  32° 
varies  from  about  7500  feet  above  the  sea  level,  as  in  some  of  the 
more  northern  districts,  such  as  the  Sentis,  to  rather  more  than 
8500  feet  in  the  more  southern,  such  as  round  the  Viso. 

Closely  connected  with  the  isothermal  of  32°  F.  is  the  snow  line, 
a  term  which  indicates  the  frontier  between  the  lower  zone  of  a 
mountain,  where  the  fallen  snow  always  disappears  from  the  sur- 
face, and  the  upper  zone,  where  it  can  lie  permanently;  or,  in  other 
words,  the  line  where,  in  respect  of  snow,  income  and  expenditure 
for  the  year  just  balance.  This  line,  as  a  rule,  lies  somewhat  above 
the  isothermal  of  32° ;  the  difference,  however,  will  be  probably 


*  Perhaps  even  this  is  a  little  under  the  mark.     In  the  Alps  it  seems  to  vary  from  the 
above  rate  to  about  i°  F.  for  330  feet. 


THE    STORY  OF  OUR  PLANET. 


rather  less  than  700  feet.  Above  this  line  the  snow  naturally 
begins  to  accumulate  in  favorable  situations,  and  a  glacier  may  be 
formed,  as  already  described.*  This  creeps  down  the  valley,  the 
rate  of  motion  depending  upon  a  variety  of  circumstances.  Its 
pace  is  quicker  in  summer  than  in  winter,  and  seems  to  depend 
partly  upon  the  size  of  the  glacier.  In  those  of  the  Alps  the  rate 
of  motion  is  about  365  feet  a  year,  but  the  great  ice  streams  of 
Greenland  advance  from  more  than  twenty  to  even  fifty  times  as 
fast.f  In  all  cases  the  middle  part  of  a  glacier,  as  with  a  river, 
moves  more  rapidly  than  the  sides,  and  the  top  than  the  bottom. 


FIG.  48.— SKETCH  MAP  SHOWING  FORMER  EXTENT  OF  ALPINE  GLACIERS  (N.  SIDE). 

By  this  differential  motion  the  mass  is  thrown  into  a  state  of  strain, 
especially  near  the  sides;  and  as  a  result  large  crevasses  are  formed, 
as  already  described. 

As  a  glacier  moves  downward  its  surface  gradually  melts.  At  the 
commencement  of  its  journey  it  may  be  augmented  occasionally  by 
fresh  falls  of  snow,  but  this  supply  constantly  diminishes,  while  the 
rate  of  expenditure  increases  as  the  glacier  moves  down  the  moun- 
tain side.  To  what  distance  it  can  descend — whether  it  can  last 
long  enough  to  trespass  upon  the  lowlands — must  obviously  depend 
upon  the  magnitude  of  the  area  from  which  its  supplies  are  drawn 
and  the  distance  to  be  traversed.  In  the  Alps,  where  the  snow  line 
is  at  nearly  8000  feet  above  the  sea,  glaciers  of  any  importance  sel- 
dom form  unless  a  considerable  area  or  "feeding  ground"  rises  for 
more  than  1000  (commonly  at  least  2000)  feet  higher.  The  greater 
glaciers  are  fed  by  large  snowfields,  which  extend  up  to  from  10,000 

*  See  page  70.  f  See  page  73. 


ICE  AS  SCULPTOR.  133 

to  1 1, ooo  feet,  and  receive  further  supplies  from  peaks  rising  yet 
higher  by  from  2000  to  4000  feet.  The  great  Aletsch  glacier,  the 
largest  in  Switzerland,  is  surrounded  by  a  jagged  line  of  peaks,  even 
the  lowest  gap  in  which  is  above  10,000  feet.  Glaciers  come  to  an 
end  in  the  Alps  at  from  3500  to  5000  feet  above  the  sea.  It  must 
be  understood  that  these  figures  are  only  rough  approximations — 
local  causes  of  variation  are  so  numerous  that  any  very  precise 
statement  is  impossible;  indeed,  any  one  glacier  is  liable  to  fluctua- 
tions which  are  not  unimportant.  Since  about  1860  the  glaciers  of 
the  Alps  have  been  diminishing  in  size.  This  has  retreated  along 
a  comparatively  level  bed  for  several  hundred  yards,  that  has  retired 
up  a  slope  and  terminates  400  or  500  feet  above  its  former  end. 
They  have  also  lost  correspondingly  in  thickness.  Their  period  of 
diminution  appears  now  to  have  ceased,  and  for  the  last  two  or 
three  years  most  of  the  Alpine  glaciers  have  been  slowly  advancing. 

As  the  ice  is  melted  by  the  heat  of  the  sun,  the  water  collects 
into  rills,  which  furrow  the  surface  of  the  glacier  and  sometimes 
form  considerable  streams.  These  sooner  or  later  are  engulfed  in  a 
fissure  and  make  their  way  beneath  the  ice  till  they  are  gathered  at 
last  into  a  single  torrent,  which  is  augmented  by  streams  descend- 
ing from  the  slopes  on  either  side,  and  finally  issues  from  a  cave  at 
the  end  of  the  glacier.  Thus  the  rock  beneath  the  ice  may  be 
carved  into  glens.  The  engulfed  stream,  as  it  plunges  downward, 
often  drills  a  vertical  shaft  through  the  glacier,  and  the  waterfall, 
aided  by  blocks  of  stone  which  have  been  accidentally  swept  into 
the  depths,  wears  out  gigantic  potholes  in  the  rock  below.  So 
these  remain  long  after  the  ice  has  melted  away  from  a  surface  of 
rock,  and  are  among  the  most  certain  indications  that  a  glacier  has 
once  passed  over  the  place.  Wonderful  examples  of  these  pot- 
holes, called  by  some  persons  "giants'  kettles,"  were  discovered  in 
making  an  excavation  near  the  noted  Lion  monument  of  Lucerne. 
Here,  close  together,  are  several  huge  hollows  in  the  soft  sandstone 
rock,  the  largest  being  about  six  yards  deep  and  eight  wide.  Bowl- 
ders a  yard  or  more  in  diameter  still  lie  within  them,  the  pestles 
which  once  ground  out  these  gigantic  mortars  (Fig.  49). 

As  the  glacier  moves  down  a  valley  it  abrades  the  rocks  beneath ; 
its  surface  is  armed  by  fragments  broken  from  projecting  ledges,  by 
stones  which  have  fallen  down  crevasses,  and  by  the  finer  powder 
which  has  been  either  worn  away  from  the  underlying  rock  or 
derived  from  the  crushing  of  chips.  Grist  never  fails  in  a  mill  like 
this,  but  very  much  of  it  comes  from  the  nether  millstone.  The 


134  THE   STORY  OF  OUR  PLANET. 

effect  of  a  glacier  upon  the  rocks  over  which  it  passes  may  be  com- 
pared  to  that  of  a  file  or  of  sandpaper.  By  degrees  all  promi- 
nences are  removed,  and  the  rough,  often  jagged,  outlines  charac- 
teristic of  ordinary  weathering  are  replaced  by  rounded  billowy  sur- 
faces, "like  the  backs  of  plunging  dolphins."  But  a  more  homely 
comparison  may  be  made,  and  one  which  long  ago  commended 
itself  to  inland  folk,  who  were  more  familiar  with  flocks  than  with 
cetaceans.  The  outline  of  these  iceworn  rocks  is  frequently  not 


FIG.  49.— BIRD'S-EYE  VIEW  OF  POTHOLES  IN  GLACIER  GARDEN,  LUCERNE. 

unlike  that  of  the  backs  of  sheep  as  they  are  lying  down,  and  from 
this  the  name  of  roches  moutonntes  was  given  (Fig.  50).  The  surface 
at  times  is  worn  quite  smooth,  even  polished  ;  but  as  Nature  is  rather 
careless  about  the  quality  of  the  putty  powder,  her  work  is  con- 
stantly marred  by  scratches  from  the  coarser  particles.  Grooves, 
and  even  shallow  channels,  are  occasionally  worn  out  by  the  pas- 
sage of  larger  stones,  so  that  the  aspect  of  a  district  from  which 
glaciers  have  retreated,*  after  it  has  been  once  seen,  is  readily 
recognized;  their  "handwriting  on  the  wall"  is  generally  so  plain 
that  he  who  runs  may  read.  It  may  be  noticed  again  and  again 
among  the  Scotch,  the  Cumbrian,  and  the  Cambrian  Highlands;  it 
can  even  be  discovered  on  the  lower  slopes  of  Arthur's  Seat,  on  the 

*  Other  signs  there  are,  such  as  moraines,  but  as  these  result  from  the  transporting,  not 
the  erosive,  force  of  a  glacier,  a  description  of  them  must  be  postponed  to  another  chapter. 


ICE  AS    SCULPTOR. 


'35 


limestone  rocks  in  Morecambe  Bay,  and  above  the  cliffs  of  the 
Northumbrian  coast.  There  was  a  time,  to  be  described  more  fully 
in  a  later  chapter,  when  glaciers  flowed  down  every  valley  of  the 
Pyrenees  and  trespassed  on  the  lowlands  of  Southern  France,  when 
they  buried  deep  the  sacred  cave  at  Lourdes  and  the  rock  crowned 


FIG.  50. — "ROCHES  MOUTONNEES" — THE  GRIMSEL. 


by  the  pilgrim  church.  Then  also,  between  the  Alps  and  the  Jura, 
instead  of  lake  and  forest,  cornfield  .and  vineyard,  was  one  wide  field 
of  ice ;  for  the  glaciers  from  the  valley  of  the  Rhone  welled  up 
against  the  slopes  of  the  Chasseron  above  the  Lake  of  Ncuchatel 
(Fig.  48). 

But  if  a  glacier  can  abrade,  can  it  also  excavate?  This  question 
during  the  last  thirty  years  has  greatly  exercised  the  minds  of 
geologists,  and  it  is  one  of  such  general  interest  as  to  call  for  a  brief 
sketch  of  the  arguments  on  both  sides.  Members  of  one  school 


136  THE   STORY  Of  OUR  PLANET. 

attribute  great  excavatory  power  to  a  glacier;  they  point  con- 
fidently to  the  subalpine  lakes  as  its  handiwork.  They  have  even 
cast  longing  glances  at  those  huge  sheets  of  water  in  North  America 
which  are  drained  by  the  St.  Lawrence.  Members  of  the  other 
concede  no  more  than  some  slight  excavatory  action  under  excep- 
tional circumstances. 

The  subalpine  lakes  were  claimed  as  results  of  glacial  excavation 
by  the  late  Sir  A.  Ramsay  in  the  year  1862.*  Starting  from  the 
admitted  fact  that  these  lakes  are  true  rock  basins,  and  within  areas 
once  occupied  by  ice,  he  disposes  of  sundry  explanations  which  had 
been  previously  offered.  They  cannot  have  been  excavated  by  the 
sea;  they  are  too  deep  to  have  been  worn  out  by  the  currents  of 
the  rivers  which  flow  through  them.  If  it  is  urged  that  they  are 
gaping  fissures  in  the  earth's  crust,  the  impossibility  of  this 
hypothesis  is  at  once  demonstrated  by  a  section  across  their  beds, 
drawn  on  a  true  scale — for  the  sides  slope  comparatively  slowly  down, 
and  the  deepest  part  sometimes  is  almost  a  plain.  They  are  on  too 
large  a  scale  and  too  numerous  to  make  it  probable  that  they  have 
been  results  of  local  subsidence  caused  by  the  removal  of  under- 
lying beds  by  any  process  of* solution — like  the  little  meres  formed 
in  Cheshire  when  the  ground  sinks  as  the  rock  salt  beneath  is 
liquified  and  carried  away  in  the  brine  springs;  nor  can  they  be 
explained  as  basin-like  depressions — great  shallow  dimples  on  the 
face  of  the  earth — formed  by  the  bending  down  of  the  strata  toward 
a  common  center,  in  which  water  has  accumulated  as  in  the  hollow 
of  a  mackintosh  cloak,  because  no  such  structure  can  be  detected 
around  them,  and  it  can  be  shown  that  the  direction  of  the  lake  is 
often  transverse  to  the  strike  of  the  outcropping  beds.  As  these 
explanations  are  unsatisfactory,  and  no  other  of  like  kind  suggested 
itself  to  the  author,  he  maintained  that  the  lake  basins  must  have 
been  made  by  something  which  was  able  to  grind  and  scoop.  This, 
he  argued,  a  glacier  can  do,  as  it  rubs  down  its  rocky  bed,  if  it  presses 
with  greater  force  on  certain  parts,  and  thus  wears  out  trough-like 
hollows,  the  form  of  which  is  modified  by  the  geography  of  the 
glacier  and  the  geological  structure  of  the  district.  In  confirmation 
of  this  view  he  called  attention  to  the  fact  that  tarns  and  lakelets  are 
abundant  in  regions  such  as  Scandinavia  and  parts  of  Scotland, 
Wales,  and  Northern  America,  over  which  it  is  universally  admitted 
that  glaciers  once  flowed ;  and  these  are  often  true  rock  basins, 

*  Quarterly  Journal  of  the  Geological  Society,  1862,  p.  185. 


ICE  AS  SCULPTOR.  137 

analogous  to,  though  on  a  much  smaller  scale  than,  those  of  the 
subalpine  lakes.  The  explanation  was  extremely  plausible ;  it  was 
undoubtedly  supported  by  a  certain  number  of  facts,  and  the  other 
hypotheses  which  were  cited  had  been  completely  overthrown.  It 
was  soon  received  into  general  favor,  and  still  counts  many  adher- 
ents. But  even  in  the  hour  of  its  greatest  popularity  it  was  stead- 
fastly opposed  by  a  smaller  number  of  geologists.  Veterans  like 
Lyell  and  Murchison  looked  askance  at  it ;  men  exceptionally 
familiar  with  the  Alps,  like  the  late  John  Ball,  like  Ruskin,  and 
others,  suggested  serious  difficulties.  It  was  asked :  If  glaciers 
were  able  to  excavate  basins,  long  as  Como  and  Maggiore,  great  as 
Geneva  and  Constance,  deep  as  Thun  and  Lucerne,  or,  in  places 
sheltered  by  lower  mountains,  as  Zug  and  Lugano,  how  was  it  that 
the  beds  of  the  valleys,  from  the  heads  of  the  present  lakes  to  the 
feet  of  the  existing  glaciers,  were  not  full  either  of  tarns  or  filled-up 
lakelets?  or,  at  any  rate,  did  not  present  in  cross  section  the  outline 
of  broad  troughs,  like  the  letter  U,  such  as  would  be  planed  out  by 
a  gouging  tool  like  a  glacier?  What,  then,  are  the  facts  which  are 
learned  by  a  careful  study  of  the  Alpine  valleys  above  these  lakes 
which  are  the  subject  of  dispute?  Wherever  its  rocky  bed  is 
exposed  to  view  it  is  found  that  not  only  are  tarns  rare,  but  also 
the  slopes  on  either  side  descend  with  comparative  steepness  to  the 
level  of  the  torrent ;  or,  in  other  words,  the  V-like  section  charac- 
teristic of  river  erosion  is  everywhere  present.  Yet  rocks  striated 
and  rounded  by  glacial  action  abound,  and  can  be  often  traced  to 
within  a  few  feet  of  the  water,  showing  that  the  contours  of  the 
district  have  not  been  materially  changed  since  the  ice  melted. 
The  glacier,  as  it  has  been  said,  "has  all  along  been  'indentured'  in 
a  groove,  but  it  has  been  a  thoroughly  idle  apprentice,  till  some 
cause,  no  more  permanent  than  the  master's  stick,  has  quickened  it 
into  intense  but  brief  energy."  A  glacier  in  its  descent  of  a  moun- 
tain valley  seems  to  have  produced  effects  which  are,  comparatively 
speaking,  superficial ;  it  has  rasped  away  prominences,  and  made 
rough  places  smooth,  but  as  an  excavator  it  has  been  a  failure,  for 
if  rocks  projected  in  its  path,  it  flowed  past  the  higher  or  over  the 
lower,  like  a  river  by  the  pier  of  a  bridge  or  over  a  bowlder  in  its 
stream ;  nay,  sometimes  it  has  not  even  removed  out  of  the  way 
loose  material,  but  has  crept  lumbering  above  it.*  The  tarns  so 

*  In  one  case,  at  the  back  of  the  town  of  Como,  it  was  so  exhausted  with  the  effort  of 
excavating  that  arm  of  the  lake,  and  climbing  afterward  up  the  hill,  that  the  crest  of  soft 
sandstone  over  which  it  flowed  still  remains  comparatively  sharp  and  unworn. — Quarterly 
Journal  of  the  Geological  Society ',  1874,  p.  485. 


138  THE  STORY  Of  OUR  PLANET. 

common  in  many  mountainous  districts,  which  the  disbelievers  in 
extensive  glacial  excavation  are  willing  to  concede  to  the  action  of 
ice,  can  be  shown  to  occur,  almost  invariably,  either  at  the  foot  of 
steep  slopes,  as  in  the  bed  of  a  corrie  on  the  mountain  side,  where 
a  somewhat  plastic  substance  like  ice  would  of  necessity  scrape  with 
considerable  force  upon  the  rocky  floor  below,  as  the  angle  of 
descent  was  changed ;  or  else  behind  barriers  and  narrow  places  in 
the  bed  of  the  valley  over  which  the  ice  had  been  forced,  where  it 
would  act  in  a  similar  way,  scraping  upon  the  rock  behind  the 
obstacle.  Lastly,  the  opponents  of  the  excavation  hypothesis 
pointed  out  that  in  his  discussion  of  its  rivals  Sir  A.  Ramsay  had 
strangely  overlooked  one  alternative — viz.,  that  the  lakes  might 
have  been  formed  by  a  subsidence,  not  local,  but  general,  affecting 
a  considerable  district  parallel  with  the  average  trend  of  the  moun- 
tain range.  To  this  none  of  the  objections  which  had  been 
advanced  could  apply.  His  critics  maintained  that  the  subalpine 
lakes  were  portions  of  valleys  which  had  been  previously  excavated 
in  the  usual  way  during  the  long  period  when  the  Alps  were  rising 
and  being  sculptured;  that  at  a  time  geologically  recent  the  same 
forces  as  had  produced  the  mountain  ranges,  by  wrinkling  and 
doubling  into  parallel  folds  a  portion  of  the  earth's  crust,  had  again 
operated,  developing  a  comparatively  slight  flexure,  which  affected 
the  level  of  the  floors  of  the  valleys.  These,  at  one  place,  may 
have  been  slightly  pushed  up;  further  back  they  may  have  curved 
gently  downward,  bending  the  sloping  floor  into  a  hollow,  in  which 
water  would  gradually  accumulate  as  the  subsidence  progressed. 
An  examination  of  a  geological  map  of  the  Alps  indicates  that  the 
majority  of  the  lakes  can  be  grouped  in  zones  connected  with  the 
trend  of  the  ranges,  like  Orta,  Maggiore,  Lugano,  Como,  Iseo,  etc.; 
and  if  the  question  be  asked,  Why,  if  this  be  the  true  explanation, 
has  not  every  Alpine  valley  a  lake  near  its  mouth?  the  answer  may 
be  returned  that  the  subsidence  was  not  necessarily  uniform,  and 
that,  as  it  is,  where  a  lake  is  wanting  a  stony  plain  usually  occurs 
to  mark  where  one  formerly  existed.  As  these  lakes  would  not  be 
of  uniform  depth,  those  which  were  the  more  shallow,  or  received  a 
greater  quantity  of  ddbris,  would  be  silted  up,  for  an  extensive  delta 
has  been  formed  at  the  head  of  every  one  of  the  lakes,  and  is 
gradually  t:espassing  on  the  water.  The  careful  study  to  which,  of 
late  years,  some  of  the  Alpine  lakes,  such  as  Constance,  Lucerne, 
Zurich,  and  Geneva,  have  been  subjected,  has  shown  that  the  sub- 
aqueous contours  of  their  basins  correspond  with  the  subaerial, 


1 40  THE   STORY  Of  OUR  PLANET. 

instead  of  being  smooth  and  featureless,  as  should  have  been  the 
case  if  they  had  been  scooped  out  by  a  glacier.  It  was  pointed  out 
from  the  first  that  as  it  was  impossible  to  attribute  such  lakes  as 
the  Dead  Sea,  the  Victoria  and  Albert  Nyanza,  Tanganyika,  with 
others  in  similar  situations,  to  the  action  of  glaciers,  some  other 
method  of  forming  rock  basins  on  a  large  scale  must  exist,  so  that 
ice  was  not  left  as  the  only  possible  alternative ;  and  of  late  years 
the  work  of  American  surveyors  and  geologists  around  the  great 
lakes  of  Canada  and  the  United  States  has  proved  to  demonstra- 
tion that  these,  though  within  a  region  once  glaciated,  form  a  sub- 
merged valley  system,  the  upper  basin  of  the  St.  Lawrence  having 
subsided  relatively  to  the  lower.  Here,  as  elsewhere,  the  debris  left 
by  the  melting  ice  has  probably  helped  in  raising  the  level  of  the 
water  by  blocking  up  old  channels  of  drainage.  Lake  Michigan, 
for  instance,  is  found  to  be  divided  by  a  subaqueous  watershed  into 
two  basins,  the  more  southern  of  which  formerly  communicated 
with  Saginaw  Bay  on  Lake  Huron  by  a  channel,  now  buried  under 
drift,  but  still  to  be  traced  eastward  across  the  broad  peninsula 
between  the  two  sheets  of  water.  The  diagram  (Fig.  51),  reprinted 
by  kind  permission  from  a  most  important  paper  by  Professor  J.  W. 
Spencer,*  will  indicate  the  facts  more  clearly  than  any  verbal 
description. 

Thus  it  appears  to  be  proved  that  though  the  effects  of  a  glacier 
are  undoubtedly  considerable,  it  acts  like  a  plane  or  a  file  rather 
than  a  chisel  or  a  gouge.  Hence  it  excavates  only  under  excep- 
tional circumstances  and  to  a  limited  extent.  The  tarns  in  moun- 
tain corries,  the  lakelets  in  mountain  valleys,  may  be  attributed  to 
the  action  of  ice,  but  not  the  broad  sheets  of  Geneva  or  Constance, 
the  deep  glens  of  Brienz  and  Thun,  or  the  radiating  arms  of  Lugano 
and  Lucerne.f 

In  all  speculations  as  to  the  effect  of  glaciers  in  past  epochs  of 
the  earth's  history  it  must  not  be  forgotten  that  their  magnitude 
in  any  region  depends  primarily  on  two  conditions,  the  one  being 
the  amount  of  precipitation,  the  other  the  area  of  land  within  the 


*  Quarterly  Journal  of  the  Geological  Society,  1890,  p.  523. 

f  It  must  not  be  understood  that  lakes  can  only  be  formed  by  the  two  operations  dis- 
cussed above.  Some  (not  usually  of  large  size)  occupy  the  craters  of  volcanoes  ;  others 
have  been  blocked,  by  lava  streams,  by  moraines,  by  the  debris  of  a  torrent,  or  by  landslips. 
Some  may  be  formed  partly  in  one  way,  partly  in  another.  Indeed,  it  is  probable  that  the 
level  of  certain  of  the  Alpine  lakes  is  somewhat  raised  by  partial  blocking  of  their  effluents 
by  debris. 


ICE  AS  SCULP  TOK.  141 

snow  line.  The  neighborhood  of  Hudson's  Bay,  or  of  Yakutsk  in 
Siberia,  is  free  from  glaciers,  because  the  snowfall  is  light,  though 
the  climate  is  so  severe  that  a  fairly  thick  stratum  of  permanently 
frozen  ground  is  struck  at  a  few  feet  below  the  surface ;  while  on 
the  western  side  of  the  New  Zealand  Alps,  notwithstanding  the 
comparatively  moderate  elevation  of  the  chain  and  the  mildness  of 
the  climate,*  the  glaciers  occasionally  descend  to  within  less  than  a 
thousand  feet  of  the  sea  level,  and  considerably  lower  than  they 
come  down  on  the  eastern  slopes,  because  of  the  heavy  precipita- 
tion from  the  vapor-laden  winds  which  blow  from  the  west.  On 
the  great  mountain  chains  which  separate  Hindustan  from  Thibet 
the  glaciers,  notwithstanding  their  aspect,  are  not  nearly  so  large 
on  the  northern  side  as  on  the  southern,  because,  as  the  vapor-laden 
air  is  traveling  from  the  latter  quarter,  precipitation  takes  place 
mainly  on  that  side.  Even  in  the  Alps  a  comparatively  small 
difference  of  geographical  position  produces  a  marked  effect.  For 
instance,  the  Gross  Glockner  is  slightly  lower  than  the  Viso,  and 
the  heads  of  the  valleys  around  the  two  mountains  must  be  nearly  at 
the  same  level  ;f  yet  the  one  is  the  culminating  point  of  a  glacier 
system,  the  other  only  overlooks  some  permanent  snowbeds. 

*  Mount  Cook,  the  highest  peak,  is  12,349  ^eet  above  the  sea,  and  there  are  several 
others  about  11,000  feet.  The  mean  temperature  at  the  sea  level  is  roughly  55°  F. ;  the 
snow  line,  therefore,  should  be  at  about  7500  feet,  or  not  very  different  from  its  level  in 
the  north  of  Switzerland  ;  but  there  is  a  large  area  just  above  it,  and  the  precipitation  on 
this  is  very  heavy,  so  the  glaciers  are  relatively  much  larger  than  in  the  Alps. 

f  Probably  in  this  respect,  or  at  any  rate  in  regard  to  the  crests  of  the  ranges,  the 
Glockner  district  has  a  slight  advantage. 


CHAPTER   V. 

ICE    AS    A    CARRIER. 

GLACIERS,  like  rivers,  act  as  agents  of  transport,  though  to  what 
extent  is  a  matter  of  dispute.  Rock  dtfbris,  small  and  large,  is 
carried  upon  the  surface,  is  embedded  in  the  ice,  is  pushed  along 
between  it  and  the  bed  of  the  valley ;  so  that,  even  in  this  respect, 
a  certain  analogy  exists  between  a  glacier  and  a  river.  As  to  the 
amount  transported  in  these  three  ways,  geologists  are  practically 
agreed  upon  the  first,  differ  little  about  the  second,  but  are  very 
much  at  issue  over  the  third.  The  reason  of  this  is  that  the  first  is 
a  matter  of  direct  observation,  the  third  is  largely  one  of  inference, 
while  the  second  partakes  of  both. 

As  a  glacier  glides  slowly  on  between  the  rocky  slopes  of  a 
valley,  its  surface  is  strewn  with  debris  which  either  tumbles  from 
the  crags  above  or  is  swept  down  by  avalanches.  The  fallen 
materials  consist  sometimes  of  dust,  small  stones,  and  bowlders, 
but  occasionally  masses  occur  which  can  be  measured  by  cubic 
yards,  and  may  be  as  big  as  a  small  cottage.  As  a  rule,  they 
come  to  rest  quite  near  to  the  edge  of  the  ice,  and  so  form  a  kind 
of  rocky  selvage  to  the  ice  stream,  by  which  they  are  slowly  swept 
onward.  These  accumulations  of  broken  debris  are  called  moraines, 
and  in  such  a  position  are  distinguished  as  "lateral."  (Fig.  52.) 
Not  seldom  much  of  the  material  is  speedily  stranded,  forming  a 
bank  at  the  side.  When  two  glens  combine  their  ice  streams  and 
form  a  single  glacier  the  right  hand  moraine  of  the  one  unites  with 
the  left  hand  moraine  of  the  other.  Thus  an  embankment  of 
broken  rock  is  formed  in  the  middle  part  of  the  glacier,  and  on 
that  account  is  called  a  medial  moraine.  Obviously  the  number  of 
medial  moraines  will  be  one  less  than  that  of  the  confluent  glaciers. 
Beneath  this  rocky  covering  the  ice  melts  much  less  rapidly  than 
when  it  is  exposed  to  the  heat  of  the  sun,  so  that  the  moraine,  after 
a  time,  is  formed  of  dt'bris  masking  a  core  of  ice.  Crevasses  dis- 
turb the  regularity  of  a  moraine.  Sometimes  it  is  almost  wholly 
engulfed  ;  the  disappearance,  however,  is  to  a  great  extent  tem- 
porary— for  though  some  blocks  may  even  reach  the  bottom  of  the 


ICE  AS  A    CARRIER,  143 

glacier,  others  do  not  get  far  down,  and  are  presently,  as  it  were, 
excreted  on  the  surface.*  But  after  the  descent  of  an  icefall  the 
bank-like  form  is  generally  lost ;  so  the  broken  rocks,  as  a  glacier 
proceeds,  tend  to  disperse,  and  toward  the  end  are  scattered  broad- 
cast over  the  surface,  sometimes  so  thickly  as  to  mask  the  ice.  At 
last,  when  it  has  melted  away,  they  fall  to  the  ground,  and  form  a 


FIG.  52. — GLACIER  WITH  MORAINE  (MER  DE  GLACE). 

"  terminal  "  moraine  at  the  foot  of  the  glacier.  If  the  ice  for  some 
time  neither  advance  nor  retire,  the  materials  for  a  considerable 
period  will  be  dropped  at  the  same  spot,  and  the  moraines,  lateral 
and  terminal,  will  be  large.  Thus  they  remain  when  a  glacier  has 
melted  away  as  monuments  of  its  former  extent  and  of  the  spots  at 
which  it  has  halted  on  its  retreat.  If  no  pause  be  made,  its  bed  is 

*  Their  reappearance  is  largely  due  to  the  melting  of  the  ice,  but  it  is  possible  that  in 
such  a  position  there  is  a  sort  of  up-cast  current  in  the  ice  itself. 


144  THE   STORY  OF  OUR  PLANET. 

strewn,  pretty  uniformly,  with  debris,  but  the  materials  are  not  at 
all  sorted  as  when  distributed  by  water,  for  blocks  large  and  small 
lie  side  by  side.  Geologists  hold  different  opinions  as  to  the  fate 
of  a  moraine  when  a  glacier  advances.  Much  of  the  material  is 
probably  pushed  before  the  ice,  but  some  may  be  overridden.  A 
well-marked  moraine  cannot  be  mistaken.  A  bank  of  debris,  some- 
times several  yards  high,*  rudely  triangular  in  section,  runs  along 
the  hillside,  gently  descending  toward  the  bed  of  the  valley,  and 
forming,  as  it  crosses,  a  curve,  with  the  apex  pointing  downward. 
Even  when  the  materials  are  scattered  and  the  bank-like  form  is  not 
retained  a  moraine  often  can  be  distinguished  both  from  ordinary 
talus — since  it  consists  of  rocks  which  occur,  not  in  the  vicinity,  but 
higher  up  the  valley — and  from  torrent  dtfbris  by  the  comparative 
rarity  of  water-worn  fragments.  Rounded  or  striated  blocks  are 
scarce  in  moraines  of  glaciers,  such  as  those  in  the  Alps,  because 
the  material  which  has  been  carried  beneath  the  ice  is  small  in 
quantity  compared  with  that  which  has  traveled  upon  it,f  but 
where  a  region  is  almost  buried  beneath  ice,  as  in  Greenland,  such 
blocks  are  doubtless  much  more  abundant.  A  certain  amount  of 
material,  large  or  small,  makes  part  of  its  journey  embedded  in 
the  ice,  and  will  also  escape  unworn,  but  the  amount  of  it  probably 
depends  on  local  circumstances,  especially  on  the  frequency  of 
"  icefalls." 

Scattered  blocks  also  occur  on  the  surface  of  a  glacier  where  a 
small  medial  moraine  has  been  dispersed  or  falling  rocks  have  come 
to  rest  after  a  longer  leap  than  usual.  These  sometimes  present  a 
rather  singular  appearance,  for  a  flattish  block  is  supported  by  a 
pedestal  of  ice,  the  whole  bearing  a  rough  resemblance  to  a  mush- 
room. The  origin  of  a  glacier  table,  as  this  is  called,  is  simple. 
When  a  thick  slab  of  rock  is  lying  upon  a  glacier,  it  protects  the  ice 
beneath  it  from  the  sun,  while  all  that  around  is  thawing;  thus  a 
pedestal  is  gradually  developed  as  the  surrounding  surface  is  lowered. 
But  the  sides  of  this  are  presently  cut  back  by  the  oblique  rays  of 
the  sun  and  by  exposure  to  the  warmer  air,  so  that  the  block  above 
overhangs  its  support  more  and  more.  At  last,  however,  it  slips 
off,  and  the  process  begins  again.  Solitary  blocks  also  are  dropped 
by  a  retreating  glacier  on  the  rocky  slopes  ;  occasionally  they  are 
left  curiously  poised  on  the  curving  hummocks.  Such  are  called 

*  From  ten  to  twenty  yards  is  common.  Occasionally  the  height  of  terminal  moraines 
may  be  measured  by  hundreds  of  feet,  but  these  are  exceptional  cases. 

f  Such  bowlders  should  be  most  abundant  in  the  lowest  part  of  the  moraine, 


ICE   AS  A    CARRIER.  '145 

"perched  blocks,"  and  in  many  instances  are  among  the  surest  cri- 
teria of  the  former  presence  of  a  glacier.  At  the  opening  of  the 
Val  d'llliez  huge  blocks  of  granitic  rock  from  the  eastern  part  of  the 
range  of  Mont  Blanc  lie  among  the  vineyards  or  are  shaded  by 
Spanish  chestnuts ;  similar  blocks  are  scattered  among  the  woods 
on  the  limestone  slopes  of  the  Jura  some  hundreds  of  feet  above 
the  Lake  of  Neuchatel.  These  prove  that,  as  already  said  (page  135), 
the  glaciers  from  the  Pyrenean  chain  once  upon  a  time  overflowed 
not  only  the  sites  of  Vevay  and  of  Chillon,  but  also  the  rich  low- 
land of  Vaud  and  the  historic  shores  of  Morat. 


FIG.  53. — GLACIER  TABLES. 

Some  debris  travels  between  the  ice  and  the  rock,  consisting  of 
engulfed,  fragments  and  of  the  finer  detritus  produced  by  the  rasp- 
ing action  of  the  glacier  on  its  bed.  This  is  designated  ground 
moraine,  or  moraine  prof onde.  The  fact  is  indubitable;  but  its  im- 
portance is  more  open  to  question.  According  to  some  geologists 
ground  moraine  may  accumulate  under  favorable  circumstances  to 
a  thickness  of  at  least  a  hundred  feet,  and  may  spread  like  a  mantle 
over  hundreds  of  square  miles.  According  to  others  it  is  a  deposit 
generally  very  limited  in  thickness,  and  often  amounts  to  no  more 
than  a  film  of  mud  or  an  interrupted  "  scatter  "  of  stones.  Beneath 
the  glaciers  of  the  Alps  there  is  but  little  ground  moraine ;  here 
and  there  a  bowlder  maybe  seen  on  its  subglacial  journey,  the 
surface  of  rock  or  of  ice  may  be  smeared  with  mud,  but  the  debris, 


146*  THE   STORY  OF  OUR  PLAXET. 

so  far  as  is  known,  simply  travels,  and  docs  not  accumulate.  A 
glacier  may  sometimes  override  its  terminal  moraine,  disturbing, 
and  to  some  extent  rearranging,  the  materials,  but  there  is  no 
evidence  to  show  that  any  such  deposit,  unless  it  be  drawn  out  so 
as  to  be  very  thin,  can  be  dragged  far.  In  such  a  case  the  glacier 
probably  would  pare  away  the  upper  part  of  the  moraine  and  then 
slide  over  the  rest,  which  would  remain  comparatively  undisturbed. 
This  fact,  at  any  rate,  is  certain— that  the  Alpine  glaciers  have 
retreated  during  the  last  thirty  years  for  some  hundreds  of  yards, 
and  have  left  exposed,  not  beds  of  clay  mingled  with  subangular 


FIG.  54. — A  PERCHED  BLOCK. 

and  striated  stones,  but  either  bowlders  and  big  pebbles,  such  as 
are  transported  by  the  torrent  a  little  lower  down  the  valley,  or  bare 
surfaces  of  ice-worn  rock,  sprinkled,  however,  occasionally  with 
ddbris  dropped  from  above  by  the  receding  glacier. 

As  a  discussion  of  the  origin  of  till  and  bowlder  clay  would  neces- 
sarily travel  beyond  the  proper  limits  of  this  chapter,  the  foregoing 
remarks  on  ground  moraine  may  suffice  for  the  present.  It  may 
possibly  exist  beneath  the  gigantic  glaciers  of  Greenland,  where, 
beyond  the  marginal  zone  of  rocky  hills,  the  ice  extends  inland  un- 
broken for  hundreds  of  miles,  and  a  stone  is  seldom  or  never  found 
on  its  surface ;  but  neither  under  the  Alpine  glaciers,  so  far  as  can 
be  seen,  nor  in  the  valleys  for  many  miles  below  their  present  ex- 
tremities, can  any  trace  be  discovered  of  a  ground  moraine  of  real 


ICE   AS  A    CARRIER.  147 

importance,  so  that,  notwithstanding  it  looms  so  large  in  literature, 
it  may  be  comparatively  a  dwarf  in  the  realm  of  fact. 

Still  the  quantity  of  debris  that  passes  beneath  a  glacier,  espe- 
cially in  the  form  of  mud,  is  considerable.  This  is  gathered  together 
by  the  water  from  the  melting  ice,  and  is  swept  into  the  main  tor- 
rent, which,  when  it  issues  from  the  ice  cave  at  the  end  of  a  glacier, 
is  always  gray  with  suspended  mud.*  It  has  been  estimated  that 
the  average  amount  of  sediment  in  the  water  of  such  a  torrent  is 
about  i  in  20,000  by  weight.  Dr.  Heimf  states  that  the  amount  of 
detritus  removed  annually  by  all  the  Justedal  glaciers  in  Norway  is 
about  equal  to  a  cube  of  rock  measuring  134^  feet  on  each  side. 
The  comparative  efficiency  of  torrents  and  of  glaciers  as  agents  of 
denudation  is  still  a  matter  of  dispute.  Dr.  Heim,  after  consider- 
ing estimates  of  the  amount  of  mud  transported  in  each  case,  is  of 
opinion  that  glacier  erosion  is  very  insignificant  in  its  effects  com- 
pared with  that  caused  by  running  water.  It  must,  however,  be 
admitted  that,  until  the  question  of  the  real  importance  of  ground 
moraine  is  settled,  no  very  satisfactory  basis  for  a  comparison  exists, 
because  it  cannot  be  determined  how  much  of  the  material  worn 
away  by  a  glacier  from  the  underlying  rock  is  carried  under  the  ice 
and  extruded  at  the  end,  so  as  to  be  kept  always  separate  from  that 
conveyed  by  the  torrent.  There  is  also  another  disturbing  factor, 
which,  however,  operates  in  the  contrary  direction.  The  glacier 
torrent  represents  more  than  the  melting  of  the  ice,  and  must  con- 
vey materials  in  addition  to  those  worn  from  the  rock  beneath. 
Streams  come  plunging  down  the  hills  on  either  side  to  burrow 
beneath  the  ice,  and  then  join  the  main  torrent.  These  must  often 
transport  considerable  quantities  of  mud  and  stones,  which  repre- 
sent the  work  both  of  other  glaciers  and  of  ordinary  erosion.  Rock 
debris  falls,  as  already  described,  on  to  the  surface  of  the  ice,  and  a 
portion  of  it  ultimately  finds  its  way  to  the  bottom,  and  may  help 
to  augment  the  contents  of  the  torrent.  Thus,  at  the  prese'nt  time, 
it  seems  hardly  possible  to  make  any  very  trustworthy  estimates,  or 
to  do  more  than  compare  the  amount  transported  by  glacier  streams 
(representing  the  total  product  of  a  certain  area)  with  that  carried 
by  a  river  which  drains  a  tract  of  about  the  same  extent,  and  of 
similar  configuration,  entirely  free  from  glaciers.  But  in  the  present 

*  The  water  is  not  only  diminished  in  quantity,  but  also  cleaner  in  the  winter  season. 

f  "  Handbuch  der  Gletscherkunde,"  a  work  full  of  valuable  facts  and  observations, 
of  which  an  excellent  summary  (by  Mr.  F.  F.  Tuckett)  is  given  in  the  Alpine  Journal, 
vol.  xii. 


ICE  AS  A    CARRIER.  149 

writer's  opinion  Dr.  Heim,  even  if  he  may  have  slightly  under- 
valued the  erosive  power  of  glaciers,  cannot  be  very  far  wrong  in 
regarding  their  action  as  less  important  than  that  of  rivers.  Cer- 
tainly the  indirect  evidence  obtained  from  the  structure  of  the  Alps, 
and  other  mountain  regions  in  the  northern  hemisphere,  points 
distinctly  toward  these  conclusions.  Striking  as  the  rounded  con- 
tours and  other  marks  of  glacial  action  may  be  in  the  valleys  above 
the  lakes,  and  especially  in  their  upper  glens,  where  the  ice  longest 


FIG.  56. — THE  FORMATION  OF  AN  ICEBERG. 

lingered,  yet  even  in  such  a  one  as  the  Hasli-thal,  which  is  almost 
proverbial  as  an  instance  of  the  effects  produced  by  glaciers,  the 
main  features  of  the  scenery  are  those  indicative  of  the  ordinary 
work  of  rain  and  rivers.  These  the  ice  has  modified  ;  it  has  abraded 
prominences  and  rounded  off  edges  ;  like  the  fickle  Roman,  it  has 
changed  rectangles  into  curves ;  but  it  has  often  failed  to  obliterate 
crags  and  terraced  rocks  which  at  no  time  can  have  been  of  any 
great  size. 

In  the  cold  circumpolar  regions,  whether  of  north  or  of  south, 
the  huge  sheets  of  inland  ice  descend  to  the  sea  in  great  rolling 
glaciers,  sometimes  several  miles  in  width.  Creeping  along  its  rocky 
floor  the  ice  for  a  time  displaces  the  water,  but  is  then  subjected  to 
an  upward  pressure,  as  the  latter  is  the  heavier.*  This  at  last  pre. 
vails ;  huge  masses  are  broken  off  the  end  of  the  glacier,  and  after 

*  A  cubic  foot  of  sea  water  weighs  about  1026  ounces,  the  same  quantity  of  ice  918 
ounces. 


15°  THE   STORY  OF  OUR  PLANET. 

a  brief  period  of  wild  flurry  the  newborn  berg  drifts  out  to  sea. 
But  the  ship  of  ice  does  not  start  on  its  voyage  without  some  cargo  ; 
mud  and  stones  are  frozen  to  its  base,  are  embedded  in  its  mass, 
perhaps  are  scattered  on  its  surface.  These  are  transported  from 
Arctic  or  Antarctic  regions  to  more  genial  climates.  As  the  bergs 
are  sometimes  of  immense  size — often  measuring  in  area  hundreds 


FIG.  57. — ICEBERGS  FLOATING  OUT  TO  SEA. 

of  square  yards,  and,  occasionally,  more  than  a  hundred  square 
miles — and  their  floating  power  is  great — for,  on  an  average,  a  cubic 
foot  of  rock  can  be  just  supported  by  a  cubic  yard  of  ice  in  sea 
water — large  quantities  of  debris  may  be  easily  carried  to  consider- 
able distances.  This  cargo  is  gradually  discharged  as  the  ice  melts. 
Thousands  of  tons  of  mud  and  of  rock  fragments  must  be  dropped 
every  year  on  the  Great  Bank  of  Newfoundland ;  but  the  bergs  travel 
much  further  to  the  south,  sometimes  wandering  down  to  the  lati- 
tude of  Madrid  (41°  N.)  ;  and  in  the  southern  hemisphere,  where 
the  floating  masses  are  often  even  larger  than  in  the  northern,  they 
come  nearer  to  the  equator  by  three  or  four  degrees. 

But  in  circumpolar  regions  ice  also  forms  in  winter  time  both  on 
the  surface  of  the  sea  and  on  the  margin  of  the  land.  The  drifting 
snow,  splashed  by  the  spray,  is  frozen  on  the  beach,  and  builds  up 


ICE  AS  A    CARRIER.  ,  IS  I 

a  terrace  called  an  ice  foot.  This  is  attached  to  the  shore,  but  the 
sea  or  "  floe  "  ice  rises  and  falls  with  the  tide.  The  latter,  however, 
may  be  stranded  on  flat  coasts  by  gales,  and  is  then  moved  up  and 
down,  wearing  and  striating  the  stones  in  the  frozen  ground,  and 
producing  on  them  the  same  effects  as  would  result  from  a  journey 
beneath  a  glacier.*  Bowlders  may  be  embedded  in  the  ice  foot,  or 
masses  of  rock,  detached  by  the  frosts,  may  fall  on  to  it  from  the 
cliffs ;  these,  at  the  coming  of  the  summer,  are  floated  away  as  on  a 
raft,  to  be  deposited  ultimately,  when  it  either  is  capsized  or  is  sunk 
by  their  weight,  upon  the  bed  of  the  sea. 

One  other  method  of  ice  transport,  though  less  important,  must 
be  mentioned.  In  regions  where  the  winters  are  very  severe  the 
ground  may  be  frozen  to  a  depth  below  the  level  of  the  bed  of  a 
lake  or  river.  Thus  when  the  temperature  of  the  whole  mass  of 
water  is  low  a  crust  of  ice,  adhering  to  stones,  mud,  etc.,  may  form 
at  the  bottom  as  well  as  at  the  top.  At  the  breaking  up  of  the 
frost  this  ultimately  floats,  and  carries  off  with  it  portions  of  the 
bottom  ddbris,  which,  in  the  case  of  a  river,  may  be  drifted  to  con- 
siderable distances. 

To  conclude :  though  the  action  of  ice,  both  as  an  agent  of  ero- 
sion and  of  transportation,  has  been  sometimes  overestimated ; 
though  it  might  almost  as  reasonably  be  called  the  maker  of  Tan- 
ganyika as  of  the  Lake  of  Geneva,  of  the  Black  Sea  as  of  Lake 
Superior;  though  bowlder  clays,  as  a  rule,  may  require  for  their 
origin  something  more  than  a  glacier,  and  ground  moraines  may  be 
greater  in  fancy  than  in  fact ;  though  the  extent  of  ancient  ice  sheets 
may  have  been  exaggerated  ;  though  they  may  have  never  taken 
complete  possession  of  the  beds  of  the  North  Sea  or  of  the  Irish 
Channel,  or  even  threatened  to  invade  the  valley  of  the  Thames ; 
though,  in  a  word,  ice  may  not  have  accomplished  all  with  which 
it  has  been  credited  in  the  poetry  of  science,  still  its  claim  to  be 
regarded  as  an  important  factor  in  sculpturing  and  modeling  the 
earth's  crust  cannot  be  contested  even  in  the  most  sober  prose. 

*Feilden,  Quarterly  Journal  of  the  Geological  Society,  vol.  xxxiv.  1878,  p.  565. 


CHAPTER  VI. 

THE   WORK   OF   THE   OCEAN— MARRING  AND    MAKING. 

THE  sea,  like  the  other  modes  of  water,  both  destroys  and  trans- 
ports. Its  chemical  action  differs  but  little  from  that  of  fresh 
water;  but  it  is  less  conspicuous,  and  perhaps,  on  the  whole,  less 
important,  destructively.  Its  waters,  like  those  of  a  river,  must 
have  a  corrosive  effect  upon  the  rocks  which  are  exposed  to  them, 
but  the  amount  of  this  is  less  easily  estimated  than  in  the  other 
case,*  The  quantity  of  mineral  salts  in  a  sample  of  sea  water  can 
be  readily  calculated,  but  it  is  less  easy  to  ascertain  how  much  of 
this  has  been  brought  down  by  rivers,  and  how  much  obtained  by 
the  sea  itself  from  the  rocks  over  which  its  waves  are  dashed  and 
its  currents  flow.  Doubtless  it  is  a  cause  of  chemical  change,  but 
this  sometimes  is  protective  rather  than  destructive,  as  when  the 
carbonate  of  lime  in  organisms  is  converted  by  its  action  into  dolo- 
mite.f  a  harder  and  more  durable  salt.  Minerals  also  are  generated, 
perhaps  indirectly,  by  its  action  on  sediments.  In  shallow  waters 
iron  sulphide  forms  so  abundantly  as  to  give  a  marked  tint  to  the 
mud  on  the  bottom ;  in  the  deep  recesses  of  the  ocean  nodules  of 
manganese  oxide  and  minute  crystals  of  various  silicates  are  formed. 
At  considerable  depths,  rather  below  two  thousand  fathoms,  the  sea 
water  undoubtedly  decomposes  the  tiny  calcareous  organisms  with 
which,  as  will  be  described  later  on,  the  ocean  bed  is  thickly  strewn, 
for  these  are  found,  on  examination,  to  become  gradually  corroded 
until  they  finally  disappear.  The  same  process  must  be  continued 
as  the  water  percolates  through  materials  which  have  previously 
accumulated,  and  siliceous  organisms  will  be  also  destroyed  in  proc- 

*  According  to  Mr.  C.  Parkinson  (Quarterly  Journal  of  the  Geological  Society r,  vol.  xl. 
1884,  p.  254)  the  chemical  action  of  salt  water  on  metallic  substances  is  very  great.  "A 
strong  iron  pipe  corrodes  to  such  an  extent  that  the  piping  can  be  cut  through  with  a 
knife  like  so  much  soap.  Marble  slabs  gradually  become  pulverized  by  the  brine,  and  all 
cements  are  eaten  away  ; "  but  the  proportion  of  salts  in  the  Worcestershire  brine  is  fully 
ten  times  as  great  as  in  sea  water. 

f  Dolomite  is  a  carbonate  of  lime  and  of  magnesia  in  the  proportion  of  54.35  of  one  to 
45.65  of  the  other. 


THE    WORK  OP   THE   OCEAN— MARKING  AND  MAKING.       i$3 

ess  of  time.  But  it  must  be  remembered  that,  though  chemical 
change  is  facilitated  by  the  presence  of  water,  there  will  be  hardly 
any  transference  of  mineral  matter  unless  the  water  actually  perco- 
lates, and  that  under  the  deeper  parts  of  the  ocean  it  must  be  as 
nearly  as  possible  at  rest.  As  it  is  strained  through  rock  filters,  sea 
water  parts  with  its  mineral  constituents,  so  that  ultimately  its  his- 
tory in  traveling  through  the  earth's  crust  becomes  identical  with 
that  of  fresh  water. 

'  The  saltness  of  the  sea  is  evidence  of  its  power  of  transport,  if  not 
of  destruction,  for  at  least  a  very  large  part  of  the  salt  is  brought 
down  into  the  sea  by  rivers.  This,  however,  must  be  uniformly 
distributed  by  diffusion  or  by  currents,  for  ocean  water  has  practi- 
cally the  same  composition  in  all  parts  of  the  globe.  True,  it  is  a 
little  more  salt  in  warm  regions  than  in  cold,  but  this  difference  is 
due  to  the  greater  amount  of  evaporation  ;  for  a  time  also  it  is  more 
brackish — at  any  rate,  near  the  surface — in  the  neighborhood  of  the 
mouth  of  a  large  river.  That  the  mineral  substances  must  be 
mainly,  if  not  wholly,  brought  down  in  solution  by  the  rivers  is 
proved  by  the  fact  that  every  sheet  of  water  for  which  there  is  no 
outlet  is  salt.  Evaporation  cannot  remove  the  solid  constituents, 
which,  as  has  been  shown,  are  present  in  greater  or  less  degree  in 
every  stream  ;  so  they  remain  behind,  artd  the  water  very  slowly, 
but  very  surely,  becomes  more  salt.  There  was  a  time,  as  is 
proved  by  the  character  of  the  fossils  which  are  found  in  beds  high 
above  the  present  level  of  the  water,  when  the  Dead  Sea  was  but 
slightly  brackish  ;  it  is  salter  now  than  it  was  when  the  kings  of 
Elam  came  down  to  harry  the  Cities  of  the  Plain.  The  ocean  also 
may  be  more  salt  at  the  present  time  than  it  was  when  the  world 
was  young ;  it  would  become  much  more  so  if  countless  millions  of 
minute  organisms  were  not  ever  drawing  from  it  the  supplies  which 
are  needed  in  the  construction  of  the  solid  parts  of  their  bodily 
frames.  The  formation  of  mineral  substances  by  the  indirect  action 
of  the  sea,  and  the  consequent  withdrawal  of  some  of  its  constitu- 
ents, proceed,  as  we  have  said,  both  in  shallow  and  in  deep  water, 
but  it  is  only  under  exceptional  circumstances  that  precipitation  on 
an  important  scale  takes  place,  the  usual  minerals  being  common 
salt  and  gypsum,  which  are  deposited  in  crystals,  isolated  masses, 
or  beds.  These,  however,  are  more  commonly  the  product  of  true 
inland  seas,  like  the  Dead  Sea  and  the, Great  Salt  Lake  of  Utah—- 
as a  rule,  the  water  of  the  ocean  is  far  from  reaching  the  saturation 
point  for  any  one  of  its  constituents,  or  for  all  of  them  together. 


154  THE   STORY  OF  OUR  PLANET. 

It  would  contain,  for  instance,  quite  five  times  as  much  carbonate 
of  lime  as  is  ever  present  in  its  waters  without  being  saturated. 
Still  whatever  is  not  withdrawn  by  organic  or  chemical  action — and 
it  is  probable  some  constituents  are  not — must  accumulate,  so  that 
the  sea  may  now  contain  more  of  certain  salts  than  in  its  earliest 
times.  But  there  may  be  less  of  others,  because  no  organisms 
then  existed  to  draw  upon  its  store  of  carbonate  of  lime  and  of 
silica. 

The  sea  acts  mechanically  by  its  waves  and  its  currents.  For 
destruction  the  former  are  generally  more  important,  for  transpor- 
tation the  latter.  Currents  in  the  sea  differ  from  rivers  on  the  land 
at  least  in  this  respect.  The  one,  like  winds,  move  on  and  through 
a  fluid  of  similar  nature,  the  others  run  in  definite  channels, 
bounded  by  a  different  material.  Accordingly  the  latter  are  more 
destructive  than  the  former;  a  great  marine  current  may  run  its 
whole  course  and  do  scarcely  any  work  in  abrading  the  bed  of  an 
ocean  or  the  shore  of  a  continent.  Still,  under  certain  circum- 
stances, the  erosive  effects  of  currents,  especially  in  shallow  seas, 
are  far  from  unimportant.  On  some  coasts  the  currents,  originated 
by  tidal  movements,  though  limited  in  duration,  cannot  but  pro- 
duce important  changes.  Twice  daily  an  estuary  like  that  of  the 
Dee,  opposite  to  Flint,  becomes  one  broad  sheet  of  water ;  in  six 
hours'  time  it  is  a  waste  of  sand,  over  which  a  few  narrow  and  very 
shallow  streams  are  wandering  seaward.  This  mass  of  water,  as  it 
moves  backward  and  forward,  and  especially  in  the  later  stages  of 
its  retreat,  must  abrade  the  shoals  and  banks  and  tend  to  sweep 
loose  material  out  to  sea.  Still  much  of  this,  especially  the  finer 
sediments,  since  the  water  shortly  moves  in  the  contrary  direction, 
will  oscillate  to  and  fro,  as  unfortunately  happens  with  the  sewage 
of  London  in  the  lower  reaches  of  the  Thames,  so  that  the  trans- 
ference seaward  will  be  gradual :  nevertheless  a  transference  there 
must  be.  Twice  daily  the  sea  runs  like  a  mill  race  through  the 
rocky  portal  which  separates  Brecqhou  from  Sark,  and  tidal  cur- 
rents hardly  less  rapid  are  generated  at  many  places  around  the 
coasts  of  the  Channel  Islands.  The  cliffs  and  skerries,  for  a  time 
at  least,  are  scoured  by  a  stream  not  less  vigorous  than  that  of  a 
rapid  river.  Crags  also  and  shores  which  are  exposed  to  the  full 
force  of  one  of  the  greater  ocean  currents,  such  as  the  Gulf  Stream, 
cannot  but  feel  the  effects,  which,  perhaps,  will  be  most  marked  in 
the  channels  between  islands  where  the  sea  bed  comes  compara- 
tively near  the  surface,  and  is  thus  swept  by  the  more  quickly  run- 


THE    WOA'A'  OF    THE    OCEAN— MARRING  AND  MAKING.        155 

ning  water.  But  as  the  great  currents  for  the  most  part  strike 
away  from  land  into  the  deeper  regions  of  the  ocean,  their  work  is 
one  of  transport  rather  than  of  destruction,  and  even  in  doing  that 
only  the  lighter  materials  are  carried  -to  any  very  great  distance, 
while  with  such  as  float  it  is  difficult  to  say  to  what  extent  they 
may  have  been  drifted  by  the  winds.  Thus  the  sea  must  play  no 


FIG.  58.— ICE-WORN  HEADLAND  IN  FJORD,  NEAR  LAURVIK,  NORWAY. 

unimportant  part  in  the  distribution  of  life,  especially  vegetable,  by 
carrying  unwilling  colonists  from  land  to  land. 

The  waves  are  the  ocean's  chief  weapon  of  destruction,  the  bat- 
tering rams  which  shatter  the  rocky  bulwarks  of  sea-girt  continents. 
Their  power  and  their  work  can  be  readily  studied  wherever  the 
land  falls  steeply  to  the  sea,  but  seldom  so  well  as  on  the  coast  of 
Norway.  Here  the  mainland  is  fringed  by  a  zone  of  rocky  islands 
of  all  sizes,  from  a  few  square  yards  to  some  miles  in  area,  and  is 
pierced  at  intervals  by  fjords.  On  the  open  sea  the  wind  may  be 
blowing  a  gale,  the  waves  may  be  running  high,  but  in  these  land- 
locked recesses  only  a  faint  measured  throb  indicates  the  tumultu- 
ous beating  of  the  great  ocean  heart.  Here,  then,  on  qvery  side 
the  rounded  domes  of  ice-worn  rock  slope  gently  down  beneath  the 
surface  of  the  fjord  (Fig.  58).  But  as  the  open  water  is  gradually 
approached,  the  smooth  surfaces  begin  to  be  scarred  by  rifts  and 
gullies  where  the  waves  have  found  the  weak  places — joints,  liter- 
ally, in  the  harness  of  the  mass  (Fig.  59).  The  sea  springs  upon 
the  obstacle,  like  a  tiger  at  an  elephant,  and  leaves  the  marks  of  its 
claws  where  the  hide  is  most  vulnerable.  Further  on  the  rifts 
become  wider  and  wider,  till  the  last  remnant  of  ice-worn  rock  dis- 
appears, and  ragged  skerries  drip  with  the  creamy  surge.  If  the 


i56 


THE   STORY  OF  OUR  PLANET. 


coast  juts  out  beyond  the  island  barrier,  its  contours  are  changed  at 
once.  The  cliffs  of  Stadtlandet,  which  front  the  swell  of  the  open 
Atlantic,  are  worn  and  torn  and  gashed  from  the  top  to  the  bottom, 
but  among  the  islands  north  and  south  the  rock  descends  to  the 
water  in  rolling  hummocks,  molded  by  the  long-vanished  ice  sheet. 


FIG.  59.— ICE-WORN  ROCK  TORN  BY  WAVES,  NEAR  LANGESUND,  NORWAY. 

The  force  of  the  waves  has  been  measured  on  some  exposed 
coasts,  and  an  idea  of  their  power  as  battering  rams  maybe  gathered 
from  the  results.  At  the  Skerryvore  lighthouse,  on  Tiree,  the 
average  pressure  during  the  six  winter  .months  has  been  estimated 
at  2086  pounds  on  the  square  foot,  the  greatest  amount  recorded 
being  6083  pounds.  Even  at  the  Bell  Rock  lighthouse,  in  the  com- 
paratively sheltered  waters  off  the  mouth  of  the  Tay,  a  pressure 
amounting  to  3013  pounds  on  the  square  foot  was  registered  between 
September,  1844,  and  March,  1845,  a"d  on  one  occasion,  during  a 
storm  in  the  month  of  November,  1827,  this  exceeded  the  record  at 
Skerryvore,  for  it  rose  up  to  6720  pounds.  On  that  occasion  the 
spray  dashed  up  to  a  height  of  117  feet.  But  on  the  Island  of 
Stroma  the  surge  has  been  known  to  make  leaps  yet  more  gigantic, 
for  during  a  storm  in  the  month  of  December,  1862,  seaweed, 
wreckage,  and  stones  were  hurled  even  up  to  the  top  of  a  cliff  200 
feet  in  height.*  On  the  shore  huge  blocks  have  been  thrust  by  the 
waves  from  their  resting  places,  or  even  wrenched  away  from  the 
crags.  Masses  a  couple  of  hundred  cubic  feet  or  more  in  volume 
have  been  rolled  along  the  beach  for  distances  of  40  or  50  yards. 

*  Several  remarkable  cases  are  given  in  Sir  A.  Geikie's  charming  volume,  "  The  Scenery 
of  Scotland,"  part  i.  ch.  iii. 


THE    WORK  OF    THE   OCEAN— MARRING  AND  MAKING.       157 

One  block  weighing  eight  tons  and  a  half  was  carried  full  60  feet 
beyond  the  usual  margin  of  high  water ;  others,  in  some  cases  even 
thirteen  tons  in  weight,  were  torn  from  parts  of  the  cliffs  as  much 
as  70  feet  above  the  surface  of  the  sea.  Little  wonder,  then,  if  the 


FIG.  60.— WAVES  BREAKING  ON  THE  BEACH. 


waves,  like  carking  care,  are  destroying  the  coast  of  Britain,  and 
this 

"  Little  world, 

This  precious  stone  set  in  the  silver  sea, 

Which  serves  it  in  the  office  of  a  wall, 

Or  for  a  moat  defensive  to  a  house," 

is  being  corroded  by  its  setting,  and  has  to  pay  blackmail  for  pro- 
tection. • 

On  the  rock-bound  coasts  the  advance,  though  sure,  is  slow.  The 
waves  break  for  many  a  year  on  the  crags  of  the  Land's  End  or  of 
the  Lizard  Head,  of  Donegal  or  of  the  Orkneys,  before  any  appre- 
ciable change  is  produced  ;  but  when  the  cliffs  consist  of  softer 
materials  the  work  of  destruction  is  much  more  rapid.  In  many 
places  on  the  eastern  coasts  of  England,  from  south  of  Flambor- 
ough  Head  to  north  of  Yarmouth,  the  cliffs,  often  from  one  to  two 
hundred  feet  high,  are  composed  of  nothing  stronger  than  a  tough 
clay,  interbedded  sometimes  regularly,  sometimes  very  irregularly, 


158  THE   STORY  OF  OUR  PLANET. 

with  sand.  Here  the  ruin  proceeds  apace.  Ravenspur,  where  Bo- 
lingbroke  landed,  has  been  washed  away ;  Beacon  Cliff,  near  Dim- 
lington,  is  disappearing  at  the  rate  of  nearly  7  feet  a  year.  The  site 
of  Roman  Cromer  lies,  it  is  said,  about  2  miles  out  at  sea,  and  destruc- 
tion progresses  rapidly  all  along  the  coast  for  some  miles  on  both 
sides  of  the  town.  At  Sherringham  there  was  in  1829  a  depth  of  20 
feet  (sufficient  to  float  a  frigate)  at  one  point  in  the  harbor  of  that 
port  where  only  forty-eight  years  before  a  cliff  50  feet  high  had 
been  standing,  with  houses  upon  it.*  The  graveyard  of  Overstrand 
is  crumbling  down  to  the  shore  ;  the  tower  of  Eccles  Church  stands 
a  lonely  ruin  on  the  level  sand  (Fig.  31).  A  few  miles  south  of 
Cromer,  in  the  month  of  April,  1892,  the  green  lines  of  springing 
corn  in  the  fields  were  cut  short  by  the  margin  of  the  cliff,  showing 
that,  since  the  time  of  sowing,  masses  of  land,  sometimes  two  or 
three  yards  wide,  had  slipped  away. 

The  coast  of  Suffolk,  of  Essex,  and  of  Kent  has  suffered  in  like 
manner.  The  annals  of  Dunwich,  since  the  days  of  Edward  the 
Confessor,  are  a  dismal  record  of  destruction — monastery,  town- 
hall,  churches  and  churchyards,  quays,  streets  and  buildings  of  all 
kinds,  neighboring  fields  and  woods,  have  been  swept  away  piece- 
meal ;  and  though  this  place  has  been  continually  retreating  inland 
for  safety,  a  small  village,  with  a  single  old  church,  represents  a 
once  flourishing  town.  The  story  of  Reculver  Church  is  not  less 
remarkable.  At  this  place,  as  at  Richborough,  the  Romans  built  a 
fortress  to  guard  the  channel  dividing  Kent  from  the  Isle  of  Thanet. 
This  became  the  residence  of  Ethelbert  when  he  gave  up  to  Augus- 
tine his  palace  in  Canterbury.  A  church  was  built  in  due  course 
about  eighty  yards  further  inland.  This,  in  the  reign  of  Henry 
VIII.,  was  about  a  mile  from  the  sea  ;  yet  in  the  year  1780  the  last 
remnants  of  the  massive  masonry  of  the  Roman  fortress  fell  down 
upon  the  beach.  By  1804  the  churchyard  itself  had  been  partly 
swept  away.  The  church  was  considered  to  be  no  longer  safe,  and 
was  dismantled ;  it  is,  however,  still  standing  at  the  verge  of  the 
cliff,  but  it  would  long  since  have  perished  if  the  value  of  its  two 
low  spires  as  a  landmark  for  sailors  had  not  induced  the  Trinity 
Board  to  construct  a  sea  wall,  by  which  the  advance  of  the  waters 
has  been  arrested. 

Instances  might  be  multiplied  from  the  eastern  and  southern 
shores  of  England.  The  Needles  of  the  Isle  of  Wight,  the  Old 

*  Full  details  of  this  and  several  other  instances  will  be  found  in  Sir  C.  Lyell's  classic 
work,  "  The  Principles  of  Geology,"  ch.  xx. 


THE    WORK  OF    THE  OCEAN— MARRING  AND  MAKING.       159 

Harry  Rocks  near  Swanage  (Fig.  61),  the  Parson  and  Clerk  at  Daw- 
lish,  every  wave-worn  skerry  on  the  coast  is  a  monument  of  the 
destructive  force  of  the  ocean.  From  some  of  these  parts  have 
been  washed  away  within  the  memory  of  living  men  ;  of  others 


FIG.  61. — OLD  HARRY  ROCKS,  NEAR  SWANAGE. 

like  losses  are  preserved  by  tradition  ;  all  are  monuments  of  similar 
deeds  which  have  no  other  record  than  in  the  undated  annals  of 
Nature. 

The  waves  wreak  their  fury  chiefly  on  the  lower  part  of  a  cliff. 
A  line  of  breakers  is  like  a  train  of  the  battering  rams  of  olden 
times  at  work  on  the  wall  of  a  castle.  Its  masonry  is  sapped  at 
the  base,  and  great  pieces  flake  off  from  the  upper  part.  But  the 
wave  is  an  assailant  yet  more  persistent  than  the  battering  ram,  for 
it  pounds  fragments  into  pebbles,  which,  perhaps,  are  hurled  as 


i6o 


THE    STORY  OF  OUR  PLANET. 


missiles  against  the  very  crag  from  which  they  were  derived.  The 
joints  in  the  rock  also,  as  stated  above,  give  an  advantage  to  the 
assailant ;  like  rifts  in  a  sea  wall,  they  weaken  the  defenses.  They 
are  deepened  and  enlarged  by  the  waves,  so  that  in  places  gaping 
fissures  scar  the  cliff.  On  part  of  the  coast  of  Skye  a  curious  effect 
is  produced  by  the  occurrence  of  rocks  differing  in  hardness.  The 
cliffs  of  the  headland  of  Strathaird  consist  of  a  calcareous  sandstone 
rather  evenly  bedded,  but  this  has  been  cut  again  and  again  by 


FIG.  62. — GULLEYS  IN  PLACE  OF  DYKES — STRATHAIRD,  SKYE. 

dykes  *  of  basalt.  These,  strange  to  say,  have  yielded  to  the  waves 
more  readily  than  the  sedimentary  rock,  with  the  result  that  the 
cliff  has  been  carved  into  a  line  of  bastion-like  masses  separated  by 
narrow  gullies.  In  other  parts  of  the  island  the  opposite  effect  has 
been  produced,  and  the  dykes  stand  up  like  walls  above  the  more 
friable  sedimentary  rocks. 

Caverns  are  frequently  excavated  by  the  waves.  It  can  be  proved 
in  many  cases,  and  is  probably  true  in  almost  all,  that  these  have  had 
their  origin  in  some  fissure  which  has  first  given  access  to  the  assail- 
ant. Sometimes  the  subterranean  channel  of  a  streamlet  may  have 
been  thus  enlarged.  Sea  caves,  however,  seem  to  be  of  two  types 
— one,  small  recesses  or  chambers,  which  penetrate  only  a  very 
short  distance  into  the  cliff,  and  may  be  nearly  as  wide  as  they  are 


*  Masses  of  eruptive  rock  which  have  flowed  into  fissures  rather  regular 
have  then  become  solid. 


in  outline,  and 


THE    WORK  OF    THE   OCEAN— MARRING  AND  MAKING.        161 

deep  ;  the  other,  narrow  and  sometimes  high  fissures,  which  can  be 
traced  into  the  land  for  many  yards.  The  former  probably  are  pro- 
duced at  parts  of  the  cliff  where  for  some  reason,  such  as  the  set  of 
a  current  or  the  effect  of  a  prevalent  wind,  the  waves  strike  with 
somewhat  exceptional  force  ;  the  latter  generally  are  more  complex 
in  their  origin,  and  to  some  extent  may  be  enlarged  by  strains  pro- 
duced by  compression  and  expansion  of  the  air.  Supposing  a  fis- 
sure to  be  already  in  existence,  the  air  within  must  be  suddenly 
compressed  into  a  comparatively  narrow  compass  whenever  a  wave 
breaks  over  its  mouth,  and  must  expand  as  rapidly  when  the  water 
falls  back.  By  this  process  pieces  of  rock  will  be  dislodged  and  the 
fissure  gradually  enlarged.  Asparagus  Island,  in  Kynance  Cove, 
affords  at  certain  states  of  the  tide  a  striking  proof  of  the  violent 
disturbance  of  the  air  in  a  fissure  of  this  kind.  The  Post  Office,  as 
the  place  is  called,  consists  of  a  couple  of  slit-like  orifices,  a  few 
inches  broad,  like  rude  letter  boxes,  on  the  face  of  a  shelving  cliff, 
down  which  one  can  scramble  without  difficulty.  If  a  piece  of  paper 
be  lightly  held  close  to  the  mouth  of  one  of  these,  it  is  suddenly 
wrenched  from  the  hand  by  a  strong  indraught  of  air,  is  sucked  into 
the  hole,  and  is  seen  no  more.  It  is,  however,  prudent  to  trust  the 
ocean  postage,  and  not  to  peer  curiously  into  the  hole  to  ascertain 
the  fate  of  the  missive,  for  in  a  few  seconds  comes  an  outward  blast 
of  air,  accompanied  by  a  copious  jet  of  spray,  or  even  of  water.  By 
climbing  somewhat  higher  the  working  of  this  peculiar  system  of 
receipt  and  delivery — which  resembles  official  impertinence  as  a  set- 
off  for  a  lost  letter — is  readily  understood.  The  island  just  at  this 
point  is  all  but  cleft  in  twain  by  a  fissure,  which  opens  seaward.  The 
waves  at  a  certain  state  of  the  tide — especially  when  the  sea  is  run- 
ning high — break  upon  the  entrance  of  the  fissure,  and  send  a  mass 
of  water  surging  up  it,  which  is  dashed  at  last  against  the  further 
end.  This  produces  the  outward  discharge  of  air  and  spray.  Then 
the  water  rolls  back  ;  by  its  sudden  fall  an  inrush  of  air  is,  produced, 
which  sucks  the  paper  through  the  hole.  Very  similar  to  this,  but 
on  a  larger  scale,  are  the  "'blowers,"  or  "  puffing  holes,"  not  uncom- 
mon on  rocky  coasts.  In  these  the  fissure  extends  upward  from 
the  sea  level  till  it  reaches  the  surface  of  the  ground  some  distance 
inland.  So  when  a  gale  is  blowing  from  the  sea,  and  the  waves  are 
breaking  high  up  on  the  shore,  the  water  rushes  up  the  chasm,  and 
jets  of  spray  leap  up  like  fountains  from  the  earth.  Such  blowers  are 
not  unfrequent  on  the  rocky  coasts  of  Cornwall,  of  Western  Ireland, 
and  of  parts  of  Scotland,  where  they  are  exposed  to  the  storms  of 


162 


THE    STORY   OF   OUR   PLANET. 


the  open  ocean.  The  "  bullers  "  (or  boilers)  of  Buchan  are  noted 
instances,  and,  according  to  Sir  A.  Gcikie,  "  magnificent  examples 
occur  among  the  Orkney  and  Shetland  Islands,  some  of  the  more 
shattered  rocks  of  these  northern  coasts  being,  as  it  were,  honey- 
combed by  sea  tunnels,  many  of  which  open  up  into  the  middle  of 
fields  and  moors."  * 

But  these  fissures  are  not  always  narrow.      In  some  cases,  where 


FIG.  63.— THE  FRYING  PAN,  CADGWITH,  LOOKING  SEAWARD. 

the  structure  of  the  rock  lends  itself  to  the  work,  the  sides  of  the 
chasm  are  rapidly  cut  back  by  the  force  of  the  waves.  As  soon  as 
the  passage  becomes  a  little  wider  than  the  doorway  the  inrushing 
water  acquires  a  swirling  motion,  and  each  wave  sweeps  round  the 
walls  of  the  cavern,  undermining  them  as  it  converts  the  corridor 
into  a  hall.  As  this  broadens,  fragments  fall  from  its  unsupported 
roof,  and  enlargement  proceeds  upward  as  well  as  sideward.  The 
usual  end  of  this  process  of  undermining  is  found  in  the  story  of  the 
Lion's  Den,  near  the  Lizard  lighthouses.  On  the  iQth  of  February, 
1847,  the  greensward  sloped  down  without  a  break  from  the  crest  of 
the  hill  to  the  edge  of  the  cliff.  Early  the  next  morning  when  the 
light-keeper  looked  out  toward  H ousel  Bay  he  perceived  that  the 

*  "  Textbook  of  Geology,"  book  iii.  part  ii.  sect.  ii.  §  6. 


THE    WORK  OF    THE   OCEAN— MARKING  AND  MAKING.       163 

sea  for  a  considerable  distance  from  the  point  was  strangely  dis- 
colored. The  mystery  was  solved  as  soon  as  he  found  that  during 
the  night  a  yawning  gulf  had  opened  out  in  the  hillside,  like  a  huge 
funnel,  terminating  in  a  rocky  shaft,  the  bottom  of  which  communi- 
cated with  the  sea  by  a  natural  archway.  The  roof  of  a  cavern  had 
suddenly  fallen  in,  and  this  fearful  gulf  was  the  result.  The  Frying 
Pan  at  Cadgwith  has  doubtless  had  a  similar  history,  but  all  record 
of  this  is  lost ;  moreover,  the  pounding  of  the  waves  below  and  the 
washing  of  the  rain  above  have  enlarged  the  chasm,  so  that  now 
a  huge  corrie-like  hollow  is  parted  from  the  sea  only  by  a  natural 
arch  which  is  just  wide  enough  at  the  top  to  support  a  narrow  path 
(Fig.  63).  The  island  of  Sark  furnishes  several  examples  of  caves 
converted  into  corridors  or  roofless  halls.  At  the  Gouliot  caves 
a  headland  is  pierced  by  branching  passages  which  can  be  entered 
from  the  land  and  lead  out  to  sea.  In  these  at  low  spring  tides 
the  walls  are  a  garden  of  "  sea  fruits,"  one  sight  of  which  repays 
a  journey  for  many  a  mile.  The  upper  parts  are  thickly  studded 
with  purple  sea  anemones,  like  huge  carbuncles,  among  which  arc 
scattered  some  of  sage-green  tint  and  others  of  pale  terra-cotta,  which 
expand  like  the  flower  of  a  chrysanthemum.  The  lower  parts  are 
clothed  with  sponges  and  corallines  and  such  like  creatures,  green 
and  pink,  orange  and  coral  red,  from  among  which  sprout  thousands 
of  little  balls,  like  white  currants,  pendent  from  a  short  and  flexible 
stem  ;  while,  besides  this  wealth  of  animal  life,  seaweeds,  brown  and 
olive  and  crimson,  clothe  the  dripping  rock,  and  wave  in  the  water 
below.  The  Creux  Derrible,  on  the  opposite  side  of  the  island,  is 
a  roofless  hall  even  more  astounding  than  the  Lion's  Den,  for  from 
the  top  of  the  orifice  on  the  hillside  to  the  bottom  of  the  walls  is 
an  almost  sheer  descent  of  at  least  150  feet,  and  two  natural  arches, 
separated  by  a  massive  pier,  give  access  from  the  beach  to  an  oblong 
hall  about  five-and-twenty  yards  wide. 

Caverns  such  as  have  been  mentioned  sometimes  bear  witness  to 
a  change  in  the  relative  level  of  sea  and  land  in  times,  geologically 
speaking,  comparatively  recent.  In  many  places  on  the  western 
coast  of  Scotland — as,  for  example,  for  nearly  a  couple  of  miles 
south  of  Brodick,  in  the  Isle  of  Arran — a  well-marked  cliff  runs  at  the 
base  of  the  hills,  and  is  separated  from  the  present  sea  margin  by  a 
level  rocky  platform,  only  a  very  few  feet  above  the  present  limit  of 
high  water.  This  cliff  is  overgrown  in  many  places  by  ivy  and 
creepers ;  brushwood  and  even  trees  have  struck  root  into  its 
crevices.  Here  and  there  at  its  base  a  recess — like  a  little  chamber — 


i64 


THE    STORY   OF   OUR   PLANET. 


may  be  discovered  ;  sea  spleenwort  and  other  ferns  spcout  from  walls 
and  roof,  grass  and  maritime  plants  half  hide  its  stony  floor.  But 
little  experience  is  needed  to  recognize  that  cliff  and  cave  alike  are 
the  work  of  the  waves,  and  that  land  herbage  now  is  growing  where 
once  the  seaweeds  were  washing  to  and  fro  in  the  water.  Similar 
proofs  of  wave  action  are  to  be  seen  here  and  there  on  the  Scotch 
coast,  and,  still  better,  in  the  northern  part  of  Norway,  in  the 
terraced  banks  of  deltas,  and  in  the  horizontal  lines  furrowed  by  the 


FIG.   64. — INLAND  CLIFF  AND  OLD  SEA-BED,  WEST  COAST  OF  SCOTLAND. 


waves  on  ice-worn  rocks.  In  the  upper  part  of  the  Alten  Fjord  the 
delta  deposit  terminates  abruptly  in  two  well-marked  lines  of  terraces, 
the  crest  of  the  higher  being  about  120  feet  above  the  water.*  In 
another  place  two  horizontal  furrows  interrupt  the  smooth  surfaces 
of  the  ice-worn  bluffs,  the  highest  being  about  150  feet  above  sea 
level. 

So,  though  the  ocean  must  limit  its  destructive  action  to  a  zone 
comparatively  narrow,  and  is  not  complementary  to  rain  and  rivers 
in  its  lines  of  work — for  the  depths  of  the  ocean,  like  those  of  a 
lake,  are  comparatively  undisturbed,  and  only  change  by  the  slow 
accumulation  of  fine  sediment  or  of  organic  remains — it  is  neverthe- 
less an  engine  of  tremendous  power  within  these  limits,  and  to  its 

*  In  some  places  four  line?  of  terraces  are  visible. 


WORK  OF    THE   OCEAN— MARRING  AND   MAKING.       165 

effects  in  modifying  the  features  of  the  earth's  surface,  stack  and 
archway,  cliff  and  cavern,  rocky  platform  and  sandy  wastes,  once 
fertile  fields,  bear  silent  but  unanimous  witness.  It  may  be  asked, 
To  what  depth  does  the  destructive  power  of  the  waves  extend  ? 
It  is,  obviously,  impossible  to  return  a  precise  answer  to  this  ques- 
tion. Much  depends  upon  local  circumstances,  such  as  the  nature 
of  the  coast,  whether  it  overlooks  a  sea  more  or  less  landlocked,  or 
is  exposed  to  the  full  surge  of  the  open  ocean,  and  the  like.  It  is 
doubtful  whether  the  waves  can  have  much  battering  power  below  a 
depth  of  some  twenty  feet  from  the  surface,  and  then  only  in 
violent  storms  and  on  exposed  coasts.  The  water,  no  doubt,  will  be 
disturbed  to  a  considerably  greater  depth.  It  is  said  that  shingle  is 
occasionally  moved  off  the  Bill  of  Portland  fifty  feet  beneath  the 
surface,  and  off  the  Cornish  coast  at  nearly  double  that  depth.  In 
the  Mediterranean  a  heavy  swell  is  said  to  be  felt  down  to  a  hun- 
dred feet,  and  a  storm  produces  some  effect  for  at  least  fifty  feet 
further,  while  at  more  than  one  locality,  in  rather  exposed  seas,  sand 
on  their  bed  is  said  to  have  been  agitated  down  to  the  hundred- 
fathom  line.*  But  though  these  movements  may  result  in  some 
slight  abrasion,  they  are,  practically,  not  of  the  slightest  importance. 
In  a  vertical  direction  the  effective  zone  of  wave  action  is  very 
limited,  and  probably  ranges  generally  from  about  three  to  five 
fathoms  beneath  low  water  mark.  Thus  the  waves  act  like  a  plane, 
and  produce  an  almost  level  surface,  interrupted,  perhaps,  here  and 
there  by  an  insulated  mass,  which,  from  its  greater  hardness,  or 
some  other  accident,  has  escaped  the  general  destruction.  The 
final  result  of  wave  work  is  well  illustrated  in  many  parts  of  the 
British  coasts,  and  best  where  the  cliffs  consist  of  rocks  which 
are  neither  very  hard  nor  very  soft.  Beneath  the  chalk  cliffs  on  the 
eastern  or  southern  coasts  a  rocky  floor  shelves  gently  seaward,  at 
low  tide,  till  it  disappears  beneath  the  water.  Indeed,  the  great 
submarine  plateau  which  extends  all  round  the  British  Isjes  to  the 
hundred-fathom  line  is,  no  doubt,  partly  a  plain  of  marine  denuda- 
tion.f  The  surface  of  the  land  sometimes  exhibits  these  plains, 
occasionally  well  preserved,  but  they  even  may  be  traced,  after  care- 
ful examination,  in  districts  where  rain  and  rivers  have  subsequently 
cut  out  valleys,  and  have  almost  obliterated  the  original  structure. 
By  many  authors  the  hills  of  Cardiganshire,  possibly  the  table-lands' 

*  Prestvvich,  "  Geology,"  vol.  i.  p.  118  ;  Fol,  Geological  Magazine,  1890,  p.  430. 
f  The  result  of  marine  denunciation  and  of  subsidence  acting  jointly.     (See  Fig.   19, 
page  53-) 


1 66 


THE   STORY  OF  OUR  PLANET. 


about  the  Moselle  and  the  Rhine,  are  regarded  as  the  last  relics  of 
similar  plains  because  of  the  general  uniformity  of  level  which  is 
displayed  by  their  higher  parts. 

The  debris  swept  away  from  the  land,  or  brought  down  to  the  sea 
by  rivers,  after  oscillating  for  a  time  to  and  fro  ultimately  settles 
down  to  rest  in  deeper  water.  The  heavier  materials  travel  but  a 
short  distance ;  shingle  beds,  where  the  land  has  not  subsided, 
commonly  lie  near  to  the  shore,  sometimes  seem  hardly  to  reach 
even  to  extreme  low  water  mark.  To  what  distance  sand  may  be 


FIG.  65.— INSULATED  ROCKS  NEAR  THE  LIZARD. 

carried  depends  greatly  upon  local  circumstances — in  rather  shallow 
seas,  where  tidal  or  other  currents  are  strong,  it  may  be  trans- 
ported to  considerable  distances  from  land  ;  but  where  the  bottom 
falls  rapidly  it  must  soon  come  to  rest.  Probably  it  is  generally 
restricted  to  a  zone  the  greatest  breadth  of  which  will  not  exceed 
twenty  miles. 

Where  the  current  of  a  river  is  checked  at  its  entry  into  the  sea 
deposit  is  rapid,  and  shoals  are  formed.  This  is  the  history  of  the 
bars  commonly  found  at  the  mouths  of  rivers,  which  are  often 
serious  obstacles  to  navigation.  At  Liverpool  the  large  ocean- 
going steamers  can  only  enter  or  quit  the  Mersey  during  about 
four  hours  on  either  side  of  high  water,  for  at  other  times  the 
channel  through  the  bar  is  too  shallow.  Access  to  the  harbor  of 
Aberdeen  was  actually  closed  after  a  storm  in  the  year  1637,  but 
fortunately  the  sea  itself  removed  the  obstacle  after  a  few  days. 
The  curious  pools  of  fresh  water,  parted  from  the  sea  by  a  bank  of 


THE    WORK  OF    THE   OCEAN— MARRING  AND  MAKING.       167 

shingle,  which  are  not  uncommon  on  the  coasts  of  Devon  and 
Cornwall,  almost  certainly  owe  their  origin  to  a  nearly  similar  cause. 
The  sea,  probably  when  the  land  stood  at  a  slightly  lower  level, 
formed  a  bar  across  the  mouth  of  a  valley  or  of  a  little  bay.  This 
has  been  since  upraised  and  enlarged,  and  the  pool  between  it  and 
the  shore  has  gradually  become  fresh,  for  it  is  fed  by  streams  from 
the  land,  and  the  percolation,  owing  to  the  fall. of  the  tide,  is  mainly 
seaward. 

But  when  a  large  and  muddy  river  enters  the  sea  the  land  almost 


FIG.  66.— SHOALS  AND  CHANNELS  AT  THE  MOUTH  OF  THE  THAMES. 

invariably  advances,  often  rapidly.  The  tide  may  sweep  the  sedi- 
ment backward  and  forward  in  an  estuary,  but  the  process  of 
silting  up  goes  on.  The  flow  of  the  tide  brings  the  water  over  the 
shallow  flats ;  but  it  runs  off  by  gravitation.  During  the  pause  a 
part  of  the  suspended  detritus  is  deposited ;  something  is  added  to 
every  shoal  and  dropped  in  every  channel.  The  plants  of  the  salt 
marsh  strike  root  into  the  silt ;  when  it  has  risen  near  to  the  high 
tide  mark  the  muddy  water  is  filtered  by  the  coarse  herbage,  and 
accumulation  is  hastened.  By  degrees  the  soil  is  raised,  at  first  by 
contributions  from  exceptionally  high  tides  or  river  floods,  then  by 
gathered  dust  or  dead  vegetation,  or  even  by  the  castings  of  worms; 
and  so  the  ground  grows,  the  mud  flat  becomes  a  salt  marsh,  the 
shoal  an  island,  which  at  last  is  linked  to  the  shore  ;  the  fringe  of 


1 68  THE   STORY  OF  OUR  PLANET. 

the  land  is  ever  pushed  seaward,  and  in  this  way  a  delta  is  formed, 
through  which,  commonly  by  more  than  one  channel,  the  river 
flows,  not  unfrequently  changing  its  principal  line  of  discharge. 
The  traveler  from  Bologna  to  Venice  passes  over  more  than  one  of 
these  almost  deserted  channels  'of  the  Po,  along  which  the  water 
creeps,  as  in  a  canal,  rather  than  flows.  But  all  along  the  coast  of 
Venetia  the  land  is,.and  has  been  from  time  immemorial,  trespass- 
ing upon  the  sea.  Of  late  years  it  has  advanced  more  rapidly, 
owing  to  the  reckless  destruction  of  the  forests  on  the  Italian  slopes 
of  the  Alps  and  the  careful  banking  of  the  Po  itself ;  the  one  has 
increased  the  amount  of  debris  swept  down  by  the  rivers,  the  other 
has  prevented  this  from  being  dispersed  over  the  plains.  The 
average  rate  at  which  the  delta  advanced  between  the  years  1200 
and  1600  A.  D.  has  been  estimated  at  about  twenty-five  meters  a 
year,  but  for  the  next  two  centuries  at  no  less  than  seventy  meters 
annually.*  Ravenna  in  the  reign  of  Augustus  was  traversed  by 
canals  :  like  Venice,  and  was  made  the  principal  station  of  the 
Adriatic  fleet.  A  new  harbor  was  constructed  at  Classis,  nearly 
three  miles  to  the  southeast,  and  the  two  places  were  united  by  a 
continuous  suburb  called  Caesarea.  Gradually  the  channels  leading 
to  the  quays  of  Ravenna  and  the  basins  of  Classis  were  silted  up,  but 
so  late  as  the  middle  of  the  sixth  century  a  noble  basilica  was 
erected  at  the  latter  place.f  Now  the  seacoast  is  nearly  six  miles 
from  Ravenna ;  Caesarea  has  been  swept  away ;  of  the  shops  and 
counting  houses  of  Classis  nothing  remains,  except  that  its  church 
still  rises  in  solitary  grandeur  on  the  wide  monotonous  plain ;  a 
fever-stricken  fen  has  replaced  a  once  busy  seaport.  Away  to  the 
east,  along  the  Adriatic  shore,  La  Pineta,  the  "  evergreen  forest, 
which  Boccaccio's  lore  and  Dryden's  lay  made  haunted  ground"  to 
Byron,  extends  almost  without  a  break  for  nearly  five-and-twenty 
miles.  Some  have  thought  that  the  "  Adrian  wave  flowed  o'er " 
the  site  of  this  "  immemorial  wood  "  when  Classis  was  a  port,  but  it 
is  mentioned  as  far  back  as  the  days  of  Theodoric.  The  alluvial 
soil  has  accumulated  to  a  depth  of  full  three  yards  about  the  base 
of  the  monument  to  this  king  of  the  Ostrogoths,  which  stands  in 
the  open  country  about  a  quarter  of  a  mile  away  from  the  wall  of 
Ravenna.  More  probably  the  low  bank  of  sand  on  which  the 
pines  are  rooted  formed,  in  classic  times,  a  chain  of  islands  like  that 


*  Lyell,  "  Principles  of  Geology,"  ch.  xviii. 
f  S.  Apollinare  in  Classe,  built  A.  n.  534-549. 


THE    WORK  OF   THE   OCEAN— MARRING  AND  At  A  KING.       169 

which  still  shelters  Venice  from  the  storms  of  the  Adriatic.  But  the 
lagoons  have  been  filled  up,  and  La  Pineta  is  now  part  of  the  main- 
land. In  some  places  along  this  coast  the  advance  has  been  yet 
more  rapid.  Adria,  once  a  seaport  of  some  consideration,  is  now 
sixteen  or  seventeen  miles  inland.  This  place,  however,  is  situated 
near  the  center  of  the  delta,  where  it  has  already  passed  beyond 
the  line  of  outer  islands  still  marked  by  a  chain  of  dunes,  and  pro- 
jects several  miles  into  the  Adriatic.  Yet,  even  in  historical  times, 
the  land  appears  to  have  been  slowly  sinking.  Venice  is  said  to 
have  subsided  six  feet*  since  its  earliest  buildings  were  erected,  but 
these  only  go  back  about  a  thousand  years,  and  the  oldest  settlement 
on  the  Venetian  islets  is  hardly  earlier  than  the  middle  of  the  fifth 
century  of  our  era.  The  weight  of  the  buildings  may  have  squeezed 
the  muddy  soil  into  a  smaller  compass,  and  account  in  part  for  the 
subsidence ;  but  there  has  been  also  a  general  sinking  of  the  land, 
for  an  artesian  well  at  Venice,  which  some  years  since  was  bored  to 
a  depth  of  572  feet,  passed  through  a  series  of  terrestrial  marshy 
deposits,  in  which  here  and  there  a  band  containing  sea  shells  was 
intercalated. 

The  delta  of  the  Rhone  has  also  been  advancing  rapidly.  Meze, 
now  on  the  border  of  an  inland  sheet  of  water,  and  about  half  a 
dozen  miles  from  the  actual  seashore,  was  an  island  some  eight- 
een centuries  since.  Notre-Dame-des-Ports,  now  two  leagues 
inland,  was  a  harbor  at  the  end  of  the  ninth  century.  Sir  C. 
Lyell  argues  for  the  probability  that  some  twenty  centuries  since, 
when  Southern  Gaul  was  conquered  by  Rome,  the  delta,  even  to 
the  north  of  Aries,  was  not  generally  habitable,  for  the  Roman 
road  from  Beaucaire  to  Beziers  bends  northward  by  Nismes, 
instead  of  following  a  straight  course  as  usual,  and  the  names  of 
all  the  places  south  of  it  are  of  Latin  origin,  while  those  on  the 
other  side  are  frequently  Celtic. 

The  Mississippi  delta  extends  far  out  into  the  Gulf  of  "Mexico. 
Its  channel  is  defined  by  "  two  narrow  banks  of  alluvium,  one  side  of 
which  is  seashore  and  the  other  river  bank.  .  .  Projecting  from 
the  continent  like  an  arm,  it  pushes  out  for  sixty-two  miles  into  the 
sea,  and  spreads  over  the  water  the  branches  of  its  delta,  like  the 
fingers  of  a  gigantic  hand.  A  Hindoo  might  well  compare  the 
extension  of  the  mouths  of  a  river  to  an  immense  flower  opening 
over  the  ocean  its  serrated  corolla."  *  This,  however,  only  accounts 

*  Reclus,  "  The  Earth."  ch.  liii.  f  Reclus.  "  The  Earth.."  ch.  liii 


176 


THE   STORY  OF  OUR   PLACET. 


for  a  part  of  the  vast  mass  of  alluvium  brought  down  by  the  Mis- 
sissippi ;  large  quantities  are  deposited  on  the  inland  surface  of  the 
wide  river  plain,  and  up  to  a  date  comparatively  recent,  before  the 
floods  were  restricted  by  embankments,*  a  very  great  proportion 
must  have  been  so  distributed.  In  Lower  Egypt,  where  the  Nile 
flood  is  too  welcome  to  the  husbandman  to  be  thus  restricted,  the 


FIG.  67.— THE  MISSISSIPPI  DELTA. 

thickness  of  the  alluvial  soil  is  slowly  but  surely  increased.  Mr. 
Horner  ascertained  that  the  Nile  mud  at  Memphis  had  gathered 
about  the  base  of  a  statue  of  Ramescs  to  a  depth  of  nine  feet  four 
inches.  •  As  the  monument  had  been  standing  for  about  3200 
years,  the  rate  of  accumulation  would  be  3%  inches  in  a  ccn- 
tury.f  The  delta  projects  into  the  Mediterranean  in  a  curve, 

*  The  total  length  of  these  is  said  to  amount  to  some  two  thousand  miles. 

f  If  a  fragment  of  burnt  brick  was  really  found  at  the  bottom  of  a  shaft  sunk  sixteen 
feet  below  the  base  of  the  pedestal,  the  first  occupation  of  this  Nile  valley  by  a  compara- 
tively civilized  race  must  be  carried  back  to  a  very  remote  period,  perhaps  thirteen  thousand 
years  ago.  Hut  be  this  as  it  may,  borings  made  a  few  years  since  at  Tantah  and  Kasr-el 
Nil  were  carried  down  through  river  mud  and  sand,  and  were  discontinued  at  the  former 
place  at  a  depth  of  eighty-four  feet  without  penetrating  through  the  delta  deposit,  so 
that  this  about  Cairo  must  be  no  small  thickness. 


THE   WORK  OF  THE   OCEAN— MARRTNG  AND  MAKING.        171 

roughly  in  the  shape  of  a  half  ellipse,  but  its  advance  here  is  less 
rapid  than  might  have  been  expected,  because  a  rather  strong  cur- 
rent sweeps  the  coast,  and  carries  away  the  mud  to  scatter  it  over 
the  bed  of  the  Mediterranean,  which  about  here  deepens  rather 
rapidly. 

This  story  might  be  repeated  of  every  river,  small  or  great,  as  it 
approaches  the  sea.  In  the  earlier  stages  of  its  history  it  tends  to 
lower  its  bed  and  the  whole  area  which  it  drains ;  in  the  later  it 
gradually  changes  its  ways,  and  proceeds  to  build  both  upward  and 
onward.  Notwithstanding  the  occasional  opposition  of  coast 


FIG.  68. — BIRD'S-EYE  VIEW  OF  THE  NILE  DELTA,  LOOKING  SOUTHWARD. 

currents,  notwithstanding  the  frequent  subsidence  of  the  delta,  a 
fact  of  which  some  notice  must  be  taken  in  a  later  chapter,  the 
process  of  building  into  the  sea  steadily  proceeds.  The  waves  fret 
the  coasts,  the  ocean  devours  the  land,  the  rivers  themselves  "  draw 
down  yEonian  hills,"  but  then  they  "  sow  the  dust  of  continents  to 
be."  Here  the  sea  makes  inroads,  there  the  coast  line  is  pushed  out- 
ward. The  forces  of  the  land  and  the  ocean  are  in  eternal  conflict 
on  the  frontier  of  their  territories.  As  in  the  wars  of  nations,  the 
result  depends  much  on  the  strength  of  the  forces  brought  into  the 
field.  The  sea  triumphs  over  islands,  and  ultimately  lays  low  the 
ramparts  of  rock-bound  coasts;  but  when  the  great  rivers  come 
down  in  their  strength  from  mountain  ranges,  as  the  barbarian 
hordes  descended  upon  the  Italian  lowlands  in  the  days  of  the 
decline  of  Rome,  they  invade  the  invader,  and  in  their  turn  conquer 
the  conqueror. 


CHAPTER    VII. 

THE   PROLETARIAT  OF   NATURE. 

THE  dawn  of  life  upon  the  earth  introduced  a  new  set  of  disturb- 
ances, initiated  a  fresh  series  of  changes.  All  the  chemistry  of 
Nature,  all  the  relationships  of  the  physical  forces,  were  affected. 
The  drama  of  the  earth's  history  became  at  once  more  complicated. 
The  intricacies  increase  with  the  development  of  will  and  the 
enlarging  powers  of  voluntary  action.  Thus  in  the  present  chapter 
it  would  only  lead  to  confusion  if  any  very  rigid  separation  were 
attempted  between  the  chemical  and  mechanical  action  of  vital 
forces,  between  the  destructive,  conservative,  and  reproductive  work 
of  living  creatures,  or  even  between  their  direct  and  their  indirect 
results.  In  all  parts  of  the  realm  of  Nature  cause  and  effect  are  so 
united,  one  change  so  inevitably  leads  up  to  another,  that  it  is  hard 
to  say  where  the  chain  of  consequences  ends  when  once  its  first  link 
has  been  wrought.  The  results  of  organic  action,  whether  destruc- 
tive or  reproductive,  if  on  a  scale  somewhat  smaller,  and  in  modes 
rather  less  conspicuous,  than  those  of  the  physical  forces,  are,  never- 
theless, of  the  highest  importance,  and  to  none  more  than  to  man 
himself.  The  destructive  effect  of  plants  and  animals,  so  far  as  may 
be,  shall  be  noticed  first.  Mosses,  lichens,  and  various  other  plants, 
by  direct  and  indirect  action,  corrode  the  surface  of  rocks ;  the  roots 
of  trees  creep  into  crevices,  and  in  growing  force  them  apart ;  the 
stem  of  the  clinging  ivy  in  Europe,  the  root  of  the  wild  fig  in  India, 
becomes  a  living  wedge  to  rend  the  masonry  into  the  joints  of 
which  it  has  gained  access.  Animals  also  there  are  which  can 
honeycomb  the  surface  of  rock.  The  sea  urchin  on  the  Biscayan 
coast  rests  within  a  saucer-like  depression,  which  it  has  excavated 
for  itself  ;  mollusks  such  as  the  Pholas,  Modiola,  and  Saxicava  dig 
deep  into  rock,  some  of  them  pierce  the  branches  of  corals,  which 
then  are  more  easily  snapped  off  by  the  waves ;  even  the  limpet  by 
long  persistence  at  the  same  spot  impresses  the  print  of  his  disk- 
like  foot  on  the  hard  surface.  Floating  wood  and  piles  are  mined 
by  the  teredo  and  other  foes.  On  the  dry  land  several  specie.5  of 


THE  PROLETARIAT  OF  NATURE.  1 73 

snail  pierce  into  limestone,  to  a  depth  sometimes  of  three  or  four 
inches.  Many  animals  are  habitual  burrowers.  Throwing  up  the 
soil  facilitates  its  removal  by  wind  and  rain,  but  by  the  breaking  up 
of  the  surface  and  the  transference  of  material  vegetable  growth  is 
made  more  easy.  The  common  earthworm,  as  the  late  C.  Darwin 
proved  in  his  book  entitled  "  The  Formation  of  Vegetable  Mold 
Through,  the  Action  of  Worms,"  plays  a  most  important  part  in  the 
transference  of  material.  "  In  the  eyes  of  most  men,"  to  quote  the 
words  of  a  reviewer,  "  the  earthworm  is  a  mere  blind,  dumb,  sense- 
less, and  unpleasantly  slimy  annelid.  Mr.  Darwin  undertakes  to 
rehabilitate  his  character,  and  the  earthworm  steps  forth  at  once  as 
an  intelligent  and  beneficent  personage,  a  worker  of  vast  geological 
changes,  a  planer  down  of  mountain  sides — a  friend  of  man."  * 
Similar  work  is  performed  by  several  other  animals,  but  it  is  not 
always  so  beneficent.  The  mole  makes  his  tunnel  and  heaps  up 
the  castings ;  mice,  rats,  rabbits,  prairie  dogs,  gophers,  and  other 
rodents  carry  on  their  work  of  burrowing  in  the  parts  of  the  globe 
which  they  severally  inhabit.  By  this  the  surface  of  the  ground  is 
loosened,  fresh  material  is  exposed  to  the  action  of  wind  and 
weather,  and  other  matter  is  buried  out  of  sight.  "  The  embank- 
ments of  the  Mississippi  are  sometimes  weakened  to  such  an  extent 
by  the  burrowings  of  the  crayfish  as  to  give  way  and  allow  the  river 
to  inundate  the  surrounding  country.  Similar  results  have  hap- 
pened in  Europe  from  the  subterranean  operations  of  rats."f  The 
constructive  habits  of  the  beaver  also  locally  derange  the  economy 
of  the  globe,  for  its  dams  arrest  the  flow  of  streams  and  convert 
shallow  valleys  into  pools  and  morasses.  It  must  not  be  forgotten 
that  the  one  word  "  food  "  connotes  a  long  series  of  destructive 
changes,  not  less  important  indirectly  than  directly.  If  a  drowned 
sheep  lies  rotting  in  the  mud  of  a  marsh,  it  initiates  one  series  of 
changes ;  if  it  has  disappeared  down  the  throat  of  an  alligator,  it 
starts  another — the  results  in  the  two  cases  being  very  different. 

But  the  protective  action  of  plants  is  also  very  great.  The  grow- 
ing herb  is  like  an  armor-plate  to  defend  the  soil  against  the 
missiles  of  the  sky  ;  the  force  of  the  rain  is  broken  by  the  leaves, 
the  loose  earth  is  bound  together  by  the  roots,  and  by  both  the  flow 
of  running  water  is  checked.  The  Brenner  railway,  where  it  runs 
along  the  mountain  side,  is  partly  supported  by  embankments.  In 
August,  1867,  when  it  was. opened  for  traffic,  the  surface  of  these 

*  "  Life  and  Letters  of  C.  Darwin,"  vol.  iii.  ch.  vi. 

f  See  Sir  A.  Geikie,  "  Textbook  of  Geology,"  book  iii.  part  ii.  sect.  iii.  §  I. 


174  THE  STORY  OF  OUR  PLANET. 

banks  consisted  of  stony  earth,  freshly  upturned.  Immense  trouble 
had  been  taken  by  the  engineers  to  protect  them  from  the  action  of 
the  mountain  storms ;  stakes  had  been  driven  into  the  earth,  and 
long  sticks  twisted  between  them  so  as  to  form  little  fences  about 
six  inches  high,  and  cover  the  bank  with  a  diagonal  network  of 
wattles,  and  in  the  interspaces — a  few  feet  in  diameter — shrubs  had 
been  roughly  planted  or  grass  had  been  sown.  By  the  summer  of 
1872  the  slopes  generally  were  covered  with  vegetation,  the  fences 
were  rotting  away  and  were  often  overgrown,  and  the  banks  were 
obviously  safe  ;  but  here  and  there,  owing  to  some  exceptional  cir- 
cumstances, the  rain  had  gained  a  temporary  victory — the  fences 
had  been  destroyed,  the  soil  washed  away — and  fresh  earth  and  new 
wattles  showed  that  this  struggle  was  continued.  The  mountain 
side  is  similarly  protected  by  its  panoply  of  herbage,  brushwood, 
and  forest ;  and  where  there  is  much  grass  on  steppe  or  prairie, 
there  dust  storms  are  impossible.  Were  it  not  for  the  restraining 
effect  of  the  marram  grass  and  other  plants  the  sand  dunes  would 
often  advance  much  further  inland,  and  convert  miles  of  fertile 
country  into  desolate  wastes.  Even  beneath  the  sea  plant  life  must 
have  some  conservative  effects.  The  waving  forests  of  seaweed 
cannot  but  check  the  force  of  waves  and  currents,  and  shield  the 
banks  and  crags  from  the  rush  of  water.  Much  is  done,  as  by  the 
forests  on  the  land,  when  calcareous  algae,  serpulse,  corallines, 
barnacles,  and  other  organisms  cover,  as  with  a  coat  of  roughcast 
plaster,  the  surface  of  the  rock,  which  cannot  be  abraded  while  the 
brunt  of  the  storm  is  borne  by  this  living  cuticle.  It  exacts,  doubt- 
less, wage  for  its  work.  Every  organism  is  a  secret  and  never  idle 
laboratory  of  chemistry,  the  products  of  which  initiate  endless 
changes,  but  the  extent  of  these  is  difficult  to  detect  and  almost 
impossible  to  estimate.  From  decaying  plants  come  various 
acids — among  them  humic  and  uric — which  combine  readily  with 
oxygen,  and  so  facilitate  the  formation  of  metallic  sulphides  and 
even  of  native  metals.  The  pyrite  (or  iron  sulphide),  which  gives  a 
dark  tint  to  many  of  the  shallow  water  marine  muds,  which  spangles 
or  burnishes  fossils,  which  glitters  in  the  lumps  of  coal,  which  occurs 
in  bright  nodules  in  chalk  or  other  rocks,  indirectly  owes  its  pres- 
ence to  the  action  of  these  organic  acids.  Nodular  masses — called 
concretions,  or  septarian  stones — are  commonly  found  in  clays  and 
shales,  and  sometimes  in  other  sedimentary  rocks.  When  one  of 
these  is  broken  open  it  usually  discloses  as  its  nucleus  some  organ- 
ism— it  may  be  a  leaf  of  a  plant,  a  shell,  or  perchance  a  bone.  This 


THE  PROLETARIAT  OF  NATURE. 


175 


has  begun  the  deposition  of  a  mineral — such  as  silica,  phosphate  or 
carbonate  of  lime,  or  carbonate  of  iron — which  has  cemented  the 
softer  materials  of  the  rock  into  a  hard,  solid  lump.  In  this,  some- 
times, cracks,  subsequently  formed,  have  been  filled  up. 

The  effect  which  the  decomposition  of  an  organism  can  pro- 
duce in  initiating  mineral  changes  may  be  illustrated  by  two 
examples — the  one  simple,  the  other 
more  complex.  For  the  former  it  is 
only  needful  to  search  in  any  district 
where  the  surface  consists  of  a  fawn- 
colored  sand,  such  as  that  of  the 
Bagshot  heaths.  Where  the  dead 
roots  of  trees  are  exposed  in  an  ex- 
cavation the  sand  around  them  is 
commonly  found  to  be  bleached  for 
a  distance  of  an  inch  or  so.  The  tint 
of  the  sand  is  caused  by  the  presence 
of  limonite  (iron  rust).  The  decay- 
ing wood  has  produced  an  acid  which 
has  attacked  the  limonite,  and 
formed  a  salt  of  iron  readily  soluble 
in  water,  which  has  then  been 
removed,  leaving  the  sand  colorless, 

as  though  it  had  been  washed  in  hydrochloric  acid  or  some 
other  bleaching  fluid.  The  other  instance  was  described 
many  years  since  in  the  "  Transactions  of  the  Geological  Society."* 
"  An  earthen  pitcher,  containing  several  quarts  of  sulphate  of  iron, 
had  remained  undisturbed  and  unnoticed  for  about  a  twelvemonth 
in  the  laboratory.  At  the  end  of  this  time,  when  the  liquor  was 
examined,  an  oily  appearance  was  observed  on  the  surface,  and  a 
yellowish  powder,  which  proved  to  be  sulphur,  together  with  a 
quantity  of  small  hairs.  At  the  bottom  were  discovered  the  bones 
of  several  mice  in  a  sediment  consisting  of  small  grains  of  pyrites, 
others  of  sulphur,  others  of  crystallized  green  sulphate  of  iron,  and 
a  black,  muddy  oxide  of  iron.  It  was  evident  that  some  mice  had 
accidentally  been  drowned  in  the  fluid,  and  by  the  mutual  action  of 
the  animal  matter  and  the  sulphate  of  iron  on  each  other  the  metal- 
lic sulphate  had  been  deprived  of  its  oxygen ;  hence  the  pyrites 
and  the  other  compounds  were  thrown  down." 

*  By    Mr.    Pepys,    "  Transactions  of  the  Geological   Society,"  ser.   i.   vol.    i.  p.  399— 
quoted  by  Sir  C.  Lyell,  "  Elements  of  Geology,"  ch.  iv. 


FIG.  69. — CONCRETIONS. 

(a)  With  the  cast  of  a  shell  in  the  interior  ; 
(b)  with  septaria,  or  cracks  filled  with 
calcareous  matter  ;  (c)  concretion  of  car- 
bonate of  iron  from  the  coal-shales  of 
Steierdorf,  Croatia. 


1 76  THE   STORY  OF  OUR  PLANET. 

But  the  effects  of  life  are  most  obvious  when  it  acts  as  a  con- 
structive force.  Myriads  of  organisms  are  silently  at  work  in 
building  up  masses  of  rock  and  adding  new  material  to  the  earth's 
crust.  Most  of  these  are  simple  in  structure,  and  occupy  a  com- 
paratively humble  place  in  a  biological  classification,  but  in  the 
realm  of  Nature  the  "  task  of  the  least "  is  ever  the  most  important ; 
to  her  "  children  of  Gibeon  "  she  looks  for  the  work  which  endures. 
By  them  carbon  is  extracted  from  carbonic  acids ;  mineral  sub- 
stances are  withdrawn  from  the  soil  and  from  water.  Upon  this 
task  plants  and  animals  alike  are  engaged  ;  into  their  structures 
these  mineral  substances  are  incorporated,  and  with  them,  when  the 
work  of  life  is  ended,  rock  masses,  often  hundreds  of  feet  in  thick- 
ness, are  partly  or  even  wholly  constructed. 

To  consider  first  the  work  of  plants.  Bitumen,  asphalt,  petro- 
leum, and  other  mineral  oils,  which  are  now  of  such  high  com- 
mercial value,  have  been  produced,  in  many  cases  at  least,  by  the 
decomposition  of  forests  of  seaweed,  which  can  hardly  have  been 
less  abundant  in  past  geological  ages  than  at  the  present  -time. 
Other  plants  may  have  sometimes  brought  about  the  same  result. 
Tiny  diatoms,  the  delight  of  the  microscopist,  have  formed,  by  the 
slow  accumulation  of  their  siliceous  cases,  beds  of  "  tripoli,"  or 
"  polishing  earth,"  which  of  recent  years  has  been  pressed  into 
the  manufacture  of  dynamite.  Certain  algae  of  extremely  low 
organization  abstract  from  water  important  quantities  of  carbonate 
of  lime.  Some,  such  as  the  nullipores,  form  branching  masses  like 
small  corals.  These  in  certain  seas  accumulate  in  considerable 
quantities.  On  the  coast  of  Norway,  for  example,  they  abound 
among  the  rocks,  and  gleam  white  on  the  bed  of  the  sea  in  shallow 
water.  Of  late  years  it  has  been  shown  that  algae  also  play  a  very 
important  though  less  direct  part  in  the  formation  of  siliceous 
matter  about  geyser  basins,  and  of  the  calcareous  travertine 
deposited  in  large  masses  by  certain  springs  and  rivers.  It  matters 
little  whether  the  water  be  hot  or  cold,  for  it  has  been  found  that 
some  of  these  plants  live  in  water  which  has  a  temperature  as  high 
as  200°  F.,  and  they  begin  to  flourish  at  one  which  is  somewhat 
lower.*  Plant  remains  may  sometimes  accumulate  in  sufficient 
quantity  to  form  very  considerable  masses ;  but  for  this  favorable 
circumstances  are  required.  The  vegetable  ddbris  in  an  old  forest 


*This  subject  is  discussed  in  a  very  elaborate  report  by  Mr.  W.  H.  Weed,  printed  in 
the  Ninth  Annual  Report  of  the  United  States  Geological  Survey. 


THE  PROLETARIAT  OF  NATURE.  177 

does  not  as  a  rule  exceed  a  few  feet  in  thickness.  The  car- 
bonaceous and  bituminous  substances  produced  by  the  decom- 
position of  plants  are  constituents  of  many  rocks,  but  accumulation 
on  any  important  scale  appears  to  be  restricted  to  swampy  districts. 
On  sandy  ground  it  is  often  remarkable  how  slight  an  effect  has 
been  produced.  Parts  of  the  moorland  of  Canrock  Chase,  in 
Staffordshire,  consist  of  a  rather  porous  gravel ;  they  have  never 
been  under  cultivation,  and,  in  all  probability,  have  been  above  sea 
level  for  myriads  of  years.  Here  countless  generations  of  wild 
plants  have  flourished  in  succession.  As  the  surface  is  covered  at 
the  present  day  with  heath  and  ling,  with  fern  and  gorse,  with 
grass  and  other  wild  herbs,  so  it  has  been  for  long  ages ;  yet  the 
earth  commonly  is  discolored  only  for  a  depth  of  a  few  inches. 
Trees  may  have  once  covered  the  ground  ;  oaks,  birches,  and  thorns 
are  still  scattered  here  and  there  on  the  slopes,  but  of  those  which 
died  a  few  centuries  ago  no  trace  is  left.  The  case,  however,  is 
different  where  water  can  stagnate.  Then,  in  temperate  or  sub- 
arctic climates,  peat  mosses  are  formed.  Such  may  be  seen  in  the 
flat  lowlands  of  Eastern  England,  though  their  area  has  been  greatly 
reduced  by  the  drainage  of  the  fens.  They  are  commoner  in  the 
colder  and  more  humid  climate  of  Scotland,  they  are  so  abundant 
as  to  be  proverbial  in  Ireland,  and  are  plentiful  in  corresponding 
situations  on  the  continent  of  Europe.  The  upper  part  of  the  bog 
consists  of  growing  mosses,  such  as  Sphagnum,  Hypmnn,  and 
Bryum,  sometimes  it  even  supports  heath  and  moorland  plants 
tolerant  of  moisture  ;  below  it  is  a  mass  of  dead  vegetables,  be- 
coming in  the  lower  part  brown  or  even  black  in  color  and  compact 
in  structure.  This  deposit  may  accumulate  to  a  depth  of  at  least 
several  feet,  and  cover  many  miles  of  country — the  Bog  of  Allen 
in  Ireland,  is  about  238,500  acres,  with  an  average  depth  of  25  feet, 
and  it  is  estimated  that  about  one-seventh  of  that  island  is 
occupied  by  peat.  When  one  of  these  bogs  is  cut  away  for  fuel  a 
layer,  composed  largely  of  fresh-water  shells,  is  sometimes  found 
beneath,  showing  that  the  morass  occupies  the  site  of  a  pool,  or 
very  commonly  the  roots  of  dead  trees  are  laid  bare  in  such  a  quan- 
tity as  to  indicate  that  it  originated  in  an  old  forest.  Sir  A. 
Geikie  *  mentions  an  interesting  case,  which  proves  not  only  this, 
but  also  that  the  peat  grows  with  comparative  rapidity.  "  In  the 
year  1651  an  ancient  pine  forest  occupied  a  level  tract  of  land 

*  "  Textbook  of  Geology,"  book  iii.  part  ii.  sect.  iii.  §  3. 


178  THE   STORY  OF  OUR  PLANET. 

among  the  hills  in  the  west  of  Ross-shire.  The  trees  were  all  dead, 
and  in  a  condition  to  be  blown  down  by  the  wind.  About  fifteen 
years  later  every  vestige  of  a  tree  had  disappeared,  the  site  being 
occupied  by  a  spongy  green  bog,  into  which  a  man  would  sink  up 
to  the  armpits.  Before  the  year  1699  it  had  become  firm  enough 
to  yield  good  peat  for  fuel."  Other  evidence  is  adduced,  proving 
that  under  favorable  circumstances  peat  increases  in  thickness,  on  a 
very  rough  average,  at  the  rate  of  at  least  an  inch  a  year. 

Important  deposits  of  vegetable  matter  are  also  formed  by  plants 
other  than  mosses.  "  Among  the  Alps,  as  also  in  the  northern 
parts  of  South  America,  and  among  the  Chatham  Islands,  east  of 
New  Zealand,  various  phanerogamous  plants  form  on  the  surface  a 
thick  stratum  of  peat."*  On  tropical  coasts  the  mangrove  swamps, 
dense  thickets  of  tangled  vegetation  and  matted  roots  descending 
into  the  water,  fringe  the  shores  even  down  to  low  tide  mark,  and 
run  far  up  into  the  inlets.  They  form  a  belt  on  the  Florida  coast 
sometimes  as  much  as  twenty  miles  in  breadth.  This  must  often 
be  one  vast  bed  of  vegetable  matter,  living  and  dead.  The  great 
Dismal  Swamp,  in  Virginia  and  North  Carolina,  is  some  forty  miles 
long  from  north  to  south,  and  twenty-five  wide,  and  is  described  by 
Sir  C.  Lyell  as  having  "  somewhat  the  appearance  of  an  inundated 
river  plain  covered  with  aquatic  trees  and  shrubs,  the  soil  being  as 
black  as  that  of  a  peat  bog.  In  its  center  it  rises  twelve  feet  above 
the  flat  region  which  bounds  it.  The  soil,  to  the  depth  of  fifteen 
feet,  is  formed  of  vegetable  matter  without  any  admixture  of  earthy 
particles.  .  .  The  surface  of  the  bog  is  carpeted  with  mosses,  and 
densely  covered  with  ferns  and  reeds,  above  which  many  evergreen 
shrubs  and  trees  flourish,  especially  the  white  cedar  (Cuprcssus 
thyoides],  which  stands  firmly  supported  by  its  long  tap  roots  in  the 
softest  parts  of  the  quagmire.  Over  the  whole  the  deciduous 
cypress  (Taxodium  distichum]  is  seen  to  tower  with  its  spreading 
top,  in  full  leaf  in  the  season  when  the  sun's  rays  are  hottest,  and 
when,  if  not  intercepted  by  a  screen  of  foliage,  they  might  soon 
cause  the  fallen  leaves  and  dead  plants  of  the  preceding  autumn  to 
decompose,  instead  of  adding  their  contributions  to  the  peaty  mass. 
On  the  surface  of  the  whole  morass  lie  innumerable  trunks  of  large 
and  tall  trees  blown  down  by  the  winds,  while  thousands  of  others 
are  buried  at  various  depths  in  the  black  mire  below."  f  This  gentle 

*  Sir  A.  Geikie,  loc.  fit. 

f  "  Principles  of  Geology,"  ch.  xliv. 


THE  PROLETARIAT  OF  NATURE.  179 

rise  toward  the  central  part  of  the  swamp  is  a  common  feature  in 
peat  bogs,  as  may  often  be  noticed  in  Ireland.  Occasionally,  after 
unusually  heavy  rain,  the  mass  swells  up  like  a  sponge,  but  as  the 
result  of  this,  owing  to  its  less  coherent  nature,  the  bog  may  burst 
and  discharge  a  flood  of  viscid  black  ooze  over  the  surrounding 
country.  The  treacherous  surface  of  the  morass  frequently  proves 
fatal  to  animals,  which  are  mired  and  engulfed,  and  the  antiseptic 
properties  of  the  material  are  exceptionally  favorable  to  the  preser- 
vation of  their  remains,  as  well  as  of  the  timber  which  it  has  covered 
up.  Of  this  the  bog  oak,  so  often  used  in  Ireland  for  ornamental 
purposes,  is  a  well-known  instance.  Other  chemical  processes  are 
set  up  by  these  changes  in  dead  vegetable  matter,  leading  to  the 
formation  of  iron  sulphides  and  carbonates.  The  former  in  process 
of  time  may  be  decomposed  and  produce  limonite  ;  *  in  short,  many 
beds  of  iron  ore  of  great  commercial  value  are,  directly  or  indirectly, 
due  to  the  action  of  plant  life. 

Lignite  and  all  the  varieties  of  coal  are  simply  great  masses  of 
vegetable  material  which,  in  the  lapse  of  ages,  have  undergone 
chemical  changes  the  earlier  stages  of  which  are  represented  by 
peat.  They  have  been  buried  beneath  hundreds,  sometimes  thou- 
sands, of  feet  of  rock,  and  so  subjected  to  great  pressure,  as  well  as 
to  a  somewhat  higher  temperature.  They  have  been  kept  moist, 
but  at  the  same  time  the  air  has  been  almost  wholly  excluded. 
By  this  treatment  the  mass  has  parted  with  a  very  large  part  of  the 
oxygen  and  hydrogen  originally  present,  so  that  in  anthracite, 
which  may  be  regarded  as  the  last  stage  of  the  ordinary  processes, 
carbon  forms  more  than  nine-tenths  of  the  whole. 

But  a  piece  of  ordinary  coal,  if  studied  under  the  microscope,  is 
seen  to  consist  of  the  remains  of  extinct  plants,  which  are  some- 
times sufficiently  well  preserved  to  be  recognized  by  the  botanist. 
The  coal  raised  in  England,  and  most  of  that  which  is  at  present 
worked  in  other  parts  of  the  world,  consists  of  the  remains  qf  plants 
of  low  organization,  such  as  the  ferns,  horsetails  (Equisetum),  and 
club-mosses  (Lyccpodtum)  of  the  present  day.  The  representatives 
of  the  second  f  and  third  \  of  these  in  the  vast  morasses  of  the 
Carboniferous  period  attained  to  a  size  which  now  would  be  deemed 
gigantic,  and  took  the  place  at  present  occupied  by  forest  trees.  § 

*  The  hydrous  peroxide  of  iron,  identical  with  the  common  "  rust  "  of  the  metal. 

f  The  extinct  Catamites. 

\  Especially  the  extinct  genera  Lepidodendron  and  Sigillaria. 

§  The  remains  of  conifers  are  occasionally  recognized,  and  these,  very  probably,  were 


i8o 


THE   STORY  OF  OUR  PLANET. 


FIG.  70. — THIN  SLICE  OF  SHALE 

FROM  KETTLE  POINT, 

LAKE  HURON. 


It  has  been  also  found  that  the  spores  of  plants  allied  to  club-mosses 
occasionally  make  up  a  considerable  part  of  a  seam  of  coal,  but  they 
are  by  no  means  always  present,  and  are  less  important  constituents 
of  fuel  than  has  been  sometimes  supposed.* 

But  from  a  very  early  epoch  in  the  earth's  history  a  more  impor- 
tant part  has  been  played  in  the  formation  of  rock  masses  by  animal 
than  by  vegetable  life.  One  effect, 
which  is  often  quite  as  much  indirect 
as  direct,  the  result  of  which  has  a 
scientific  and  a  commercial  interest  dis- 
proportionate to  its  bulk,  is  the  forma- 
tion of  certain  deposits  rich  in  phos- 
phate of  lime.  Beds  of  guano  are 
produced  by  the  accumulated  excreta 
of  sea  birds  ;  phosphate  of  lime  is  also 
the  chief  constituent  in  the  bones  of 
vertebrate  animals,  and  enters  largely 
into  the  composition  of  the  solid  parts 
of  some  invertebrates,  especially  the 
Crustacea  ;  by  it,  accordingly,  these  and 

(Greatly   magnified.)    Showing  the  little  .  . 

globular  spore-cases  scattered  through  it.    other   organisms   are   sometimes    mm- 
eralized,  and  the  mud  in  their  vicinity  is 

impregnated  and  formed  into  nodules  by  a  process  of  concentration, 
which  occurs  in  Nature  with  many  other  mineral  substances.  This 
is  the  origin  of  the  so-called  "  coprolite  beds,"  which  of  late  years 
have  been  largely  worked  for  artificial  manures,  f 

At  the  present  day,  as  in  the  past,  foraminifera  rank  among  the 
most  important  contributors  to  the  production  of  marine  limestone. 
They  are  commonly  found  mingled  with  the  broken  shells  and 
its  other  constituents,  and  even  in  the  case  where  the  rock  is  com- 
posed of  masses  of  coral,  as  will  be  presently  described,  they  may 
help  in  filling  up  the  intervals  between  the  more  branching  forms. 

more  abundant  in  the  upland  districts,  but  it  is  unlikely  that  the  dicotyledons,  to  which 
sub-class  most  of  the  living  forest  trees,  especially  in  temperate  climates,  belong,  were  in 
existence  at  this  period. 

*  Cannel  coal,  a  very  inflammable  variety,  which  burns  with  a  bright  flame,  often  in 
sudden  jets,  and  does  not  soil  the  fingers  when  it  is  handled,  is  supposed  to  have  been  a 
kind  of  vegetable  mud,  produced  by  the  maceration  of  leaves,  etc!,  in  ponds. 

f  The  name  is  a  misnomer,  for  the  fossils  are  not,  as  a  rule,  the  petrified  excreta  of  ani- 
mals. The  most  important  deposits  are  in  the  Lower  Greensand  of  Bedfordshire  and  Cam- 
bridgeshire, at  the  base  of  the  chalk  in  the  Cambridgeshire  district,  and  in  the  Pliocene 
strata  of  the  eastern  counties. 


THE  PROLETARIAT  OF  NATURE.  181 

But  rocks  like  these,  which  are  formed  in  comparatively  shallow 
waters,  are  composed  chiefly  of  larger  organisms ;  and  as  the  sea  bed 
deepens,  the  work  of  the  foraminifera  becomes  more  and  more 
important.  Generally  they  are  very  minute  ;  a  large  number  of 
species,  including  some  of  the  most  abundant,  do  not  attain  the  size 
of  an  ordinary  pin's  head,  though  occasionally  one  of  the  more  disk- 
like  forms  is  rather  broader  than  a  threepenny  piece.  Such  a  one, 
however,  must  be  regarded  as  a  giant,  though  in  a  past  epoch  of 


FIG.  71.— A  LIVING  FORAMINIFER  (Miliola), 

geology  foraminifera  have  existed  which  were  even  larger  than  a 
florin,  and  occasionally  at  least  three  or  four  times  as  thick  toward 
the  middle.  These  creatures  build  up  chambered  structures  some- 
times of  singular  beauty  and  complexity,  composed,  in -a  large 
number  of  cases,  of  carbonate  of  lime,  with  which  they  are  able  to 
furnish  themselves  from  the  sea  water,  yet  the  structure  of  their 
bodies  is  singular  in  its  simplicity — "  sans  eyes,  sans  teeth,  sans 
[almost  literally]  everything."  They  are  little  more  than  tiny  lumps 
of  animated  jelly,  unprovided  with  a  skin  outside  or  a  stomach 
inside — the  only  interruption  to  their  uniformity  being  one  or  two 
minute  hollows  filled  with  an  oil-like  fluid,  and  one  part,  called  the 
nucleus,  which  is  rather  more  solid  than  the  rest.  One  of  these 
foraminifera,  which  plays  a  most  important  part  in  rock  building, 


1 82  THE   STORY  OF  OUR  PLANET. 

bears  the  name  Globigerina.  Its  calcareous  shell  is  formed  of 
chambers,  about  nine  in  number,  globular  or  slightly  oval  in  form, 
with  a  hole  at  one  end.  The  oldest  of  these  is  the  smallest,  and 
from  this  they  go  on  increasing  in  size,  being  arranged  on  a  spiral 
curve,  with  their  apertures  turned  inward,  so  as  to  open  into  a  central 
hollow.  The  wall  of  each  chamber  is  pierced  by  a  number  of  per- 
forations, and  the  outer  apertures  are,  as  it  were,  fenced  one  from 
another  by  low  walls  of  shelly  material,  from  the  common  angles  of 


FIG.  72.— A  LIVING  CHAMBERED  FORAMINIFER  (Pulvimtlina). 

which  long  and  delicate  spines  project.  From  these  holes  portions 
of  the  animal  protrude  as  trailing  threads  of  living  jelly  (Fig.  72). 
Yet  notwithstanding  such  an  elaborate  structure — and  even  this  is 
simple  compared  with  that  of  some  foraminifera — the  shell  of  glo- 
bigerina  (not  reckoning  the  spines,  which  are  generally  broken  off) 
is  so  small  that  it  would  take  almost  thirty  of  them,  placed  end  to 
end,  to  make  up  an  inch.  In  the  warmer  seas  the  ocean  water  is 
often  almost  alive  with  these  and  other  tiny  organisms,  all  of  them 
humble  in  structure,  but  not  in  every  case  calcareous.  Among 
those  composed  of  this  material  extremely  minute  lime-secreting 
algae  are  very  abundant — little  balls  invisible  to  the  naked  eye,  the 
solid  parts  of  which  may  be  compared  in  one  case  to  a  shirt  stud 


THE  PROLETARIAT  Of  NATURE.  183 

(Fig.  74),  in  another  to  a  kind  of  club,  the  little  disks  in  the  former 
being  one  twenty-five  hundredth  of  an  inch  in  length.  Among  the 
siliceous  organisms  are  diatoms,  already  mentioned,  and  tiny  ani- 
mals, somewhat  resembling  the  foraminifera,  with  "  skeletons " 
rather  less  complicated,  but,  if  possible,  even  more  beautiful. 


FIG.  73. — THE  SHELL  OF  A  GLOBIGERINA. 

These  are  called  Radiolaria.  Some  sponges  also  secrete  considerable 
quantities  of  silica  in  the  form  of  spicules  (Fig.  76),  of  which  the 
exquisitely  beautiful  Venus'  flower  basket  *  is  a  notable  example. 
In  others  the  spicules  are  calcareous,  and  in  a  third  group,  such  as 
the  ordinary  bath  sponges,  they  consist  of  a  horny  substance. 
Sponges,  however,  usually  grow  on  the  sea  bed,  and  are  only  acci- 

*  F.iiplecttlla  speciosa. 


184 


THE   STORY  OF  OUR  PLANET. 


dentally  found  floating ;  but  many  of  the  foraminifera,  especially 
globigerina,  are  tenants  of  the  upper  waters  of  the  ocean,  and  it  is 
doubtful  whether  they  live  at  depths  exceeding  about  five  hundred 
fathoms.  The  radiolaria  have  been  found  alive  at  far  greater  depths, 
and  it  is  now  generally  supposed  that  they  occupy  two  zones  in  the 
ocean  water — one  at  the  top,  like  to,  but 
possibly  even  deeper  than,  that  tenanted  by 
the  foraminifera,  the  other  extending  up- 
ward for  some  distance  from  the  bed  of  the 
ocean,  though  whether  this  zone  invariably 
exists  perhaps  may  be  open  to  question. 
Thus  if  anyone  could  walk  on  the  ocean 
floor,  say  at  the  depth  of  a  thousand  fathoms, 
myriads  of  organisms,  chiefly  globigerina, 
would  be  floating,  like  a  living  cloud,  three 
thousand  feet  above  his  head,  and  this  cloud 
would  extend  upward  for  the  same  distance 
— that  is,  to  the  very  surface  of  the  water. 
But  the  foraminifera  are  subject  to  the  uni- 
versal law  no  less  than  the  highest  of  organ- 
ized beings:  if  "  every  moment  dies  a  man," 
in  the  same  brief  time  perish  hosts  of 
globigerina.  One  part  of  their  task  ended,  another  begins.  Slowly, 
very  slowly,  they  drop  downward  through  the  still  waters.  A  never- 
ceasing  rain  of  its  dead  shells,  light  as  the  dust  which  drops  unfelt 
from  the  atmosphere,  patters  down  silently  and  incessantly  on  the 
ocean  floor.  Below  the  limits  of  shore  deposits — whether  these 
consist  chiefly  of  the  larger  organisms,  or  be  simple  rock  detritus — 
the  bed  of  the  sea,  down  to  a  great  depth,  is  covered  with  a  gray 
ooze,  which  proves  on  examination  to  be  largely  composed  of  the 
shells  of  globigerina.*  So  it  often  continues  down  to  about 
2000  fathoms,  but  on  passing  beyond  this  limit  a  change  may 
be  noticed  in  the  appearance  of  the  foraminifera.  At  first  they 
show  signs  of  corrosion.  Then  they  begin  to  look  decomposed — 
a  yellow  tinge  comes  over  the  gray,  and  this  turns  gradually,  as  the 


FIG.     74.—  (a,    b)    Cocco- 

LITHSJ  (f)  COCCOSPHERES. 
(Greatly  magnified.) 


*"  Under  the  microscope  the  surface  layer  (at  a  depth  of  2435  fathoms  in  the  Bay  of 
Biscay)  was  found  to  consist  chiefly  of  entire  shells  of  Globigerina  bulloides,  large  and 
small,  and  fragments  of  such  shells,  mixed  with  a  quantity  of  amorphous  calcareous  matter 
in  fine  particles,  a  little  fine  sand,  and  many  spicules,  portions  of  spicules,  and  shells  of 
radiolaria,  a  few  spicules  of  sponges,  and  a  few  frustules  of  diatoms." — C.  W.  Thomson. 
"The  Depths  of  the  Sea,"  ch.  ix. 


TffE  PROLETARIAT  OF  MATURE.  185 

depth  increases,  to  a  red.  Somewhat  below  2500  fathoms  the 
character  of  the  deposit  is  completely  altered :  the  foraminifera 
have  disappeared,  and  with  them  the  calcareous  elements,  so  that 
at  a  depth  of  about  3000  fathoms  it  is  a  kind  of  red  clay.  Only 
siliceous  organisms,  such  as  radiolaria,  now  remain,  which  in  some 
parts  of  the  Pacific  Ocean  are  sufficiently  abundant  to  give  a  marked 


FIG.  75.  —  A  RADIOLARIAN  (Haliomma). 

(Magnified  200  diameters.) 


character  to  the  deposit.  This  red  clay  extends  downward  to  the 
greatest  known  depths.  Even  here,  some  27,000  feet  below  the 
surface,  the  sea  bed  is  not  wholly  without  life.  With  the  red  clay 
the  tubes  of  an  annelid  have  been  dredged  up  ;  *  the  existence  of 
an  abyssal  fauna  is  a  fact,  though  its  members  are  not  numerous 
either  in  species,  genera,  or  individuals.  The  "red  clay"  also  con- 
tains nodules  of  manganese  oxide,  which  commonly  have  as  their 
nucleus  a  shark's  tooth,  *bone,  or  even  a  bit  of  pumice  ;  and  through- 

*  At  a  depth  of  about  eighteen  thousand  feet  in  the  Atlantic,  approaching  Sombrero.  — 
C.  W.  Thomson,  "  Voyage  of  the  Challenger"  ch.  iii. 


1 86  THE   STORY  OF  OUR  PLANET. 

out  all  the  deep-sea  deposits  small  fragments  of  minerals  and  of 
volcanic  rocks  with  particles  referred  to  terrestrial  and  meteoric 
dust  are  found. 


FIG.  76.— HOLTENIA  CARPENTERI. 

(Half  natural  size.)     A  siliceous  sponge  in  the  position  of  growth. 

In  some  parts  of  the  ocean  bed — as,  for  instance,  in  the  Agulhas 
Bank,  south  of  the  Cape  of  Good   Hope — the   tests   of  the   dead 


THE  PROLETARIAT  Of  NATURE.  187 

foraminifera  are  occupied  by  more  than  one  variety  of  a  hydrous 
silicate.  The  commonest  is  glauconite,  a  mineral  of  a  strong  green 
color,  which  has  for  its  bases  chiefly  iron  and  alumina,  with  some 
soda  and  potash.  The  casts  thus  taken  are  often  extraordinarily 
perfect,  even  the  forms  of  minute  tubules  being  preserved.  Some- 
times glauconite  alone  remains,  the  shell  having  perished.  Many, 
if  not  all,  of  the  roundish  green  grains  so  common  in  certain  sedi- 
mentary rocks,  especially  in  the  so-called  Greensand,  have  had  this 
history.  The  origin  of  the  red  clay  has  given  rise  to  much  differ- 


FIG.  77. — GLAUCONITIC  CAST  OF  A  CHAMBERED  FORAMINIFER,  SHOWING  THE 
PASSAGES  BETWEEN  THE  CHAMBERS. 

ence  of  opinion,  and  the  question  cannot  be  regarded  as  finally 
settled.  This  material  was  at  first  supposed  to  be  the  almost  im- 
palpable mud  swept  far  out  to  sea  by  the  greater  rivers  of  the  world, 
especially  those  of  South  America,  but  this  hypothesis  soon  proved 
inadequate  to  account  for  its  geographical  distribution  and  its 
relation  to  the  actual  depth  of  the  ocean.  The  suggestion  was 
afterward  made  that  the  tests  of  the  globigerina  and  its  associates, 
instead  of  consisting  of  perfectly  pure  calcite  might  contain,  em- 
bedded in  it,  a  certain  quantity  of  clayey  material,  just  as  many 
foraminifera  construct  for  themselves  a  covering  which  is  almost 
wholly  composed  of  grains  of  sand  cemented  together.  If  this 
were  so,  a  residual  clay  would  be  left  after  the  test  had  been  destroyed 
by  the  action  of  water.  Others  often  look  upon  the  clay  as  either 
a  direct  precipitate  in  the  test,  like  the  glauconite  already  mentioned, 
or  the  result  of  an  alteration  of  that  mineral ;  but  the  scientific 
men  engaged  on  the  Challenger  expedition  came  at  last  to  the  con- 
clusion that  the  red  clay  was  mainly  produced  by  the  decomposition 


1 88  THE   STORY  OF  OUR  PLANET. 

of  inorganic  material,  such  as  the  pumice  discharged  into  the  air 
during  volcanic  eruptions,  which  after  long  floating  about  on  the 
surface  of  the  sea  must  become  waterlogged  and  sink,  together  with 
the  various  kinds  of  dust  already  mentioned.  The  evidence  which 
they  cite  indicates  that  this  red  clay  accumulates  very  slowly,  and 
that  it  owes  much  to  the  above  materials ;  but  that  some  part  of  it 
may  be,  directly  or  indirectly,  due  to  chemical  action  does  not  seem 
improbable. 

In  shallower  water  the  shells  of  mollusks,  and  in  certain  localities 
reef-building  corals,  often  form  important  masses  of  rock.  The  first 
are  less  dependent  on  climate  and  other  contingencies  than  the 
second  ;  still  large  accumulations  of  shells  are  more  frequent,  on 
the  whole,  in  warm  than  in  cold  seas.  Professor  A.  Agassiz,  for 
instance,  thus  describes  the  extraordinary  abundance  of  mollusks 
and  other  marine  life  near  the  Florida  Keys.  After  stating  that 
previous  writers  had  called  attention  to  "  the  formation  of  an 
immense  submarine  plateau,  directly  in  the  track  of  the  Gulf  Stream, 
by  the  accretions  of  the  solid  parts  of  mollusks,  echinoderms,  corals, 
halcyonoids,  annelids,  Crustacea,  and  the  like,  which  have  lived  and 
died  upon  it,"  thus  furnishing  limestone,  he  goes  on  to  say,  "  No  one 
who  has  not  dredged  near  the  hundred-fathom  line  on  the  west  coast 
of  the  great  Florida  plateau  can  form  any  idea  of  the  amount  of  ani- 
mal life  which  can  be  sustained  upon  a  small  area  under  suitable  con- 
ditions of  existence.  It  was  no  uncommon  thing  for  us  to  bring  up 
in  the  trawl  or  dredge  large  fragments  of  the  modern  limestone  now 
in  process  of  formation,  consisting  of  the  dead  carcasses  of  the  very 
species  now  living  on  the  top  of  this  recent  limestone."  *  Indirectly 
also  that  which  has  lived  augments,  through  the  intervention  of  that 
which  still  lives,  the  accumulating  calcareous  masses,  since  certain 
holothurians,  echinoderms,  and  fishes  browse  upon  the  branches  of 
living  corals  and  other  organisms  which  possess  similar  solid  parts, 
and  the  material,  after  passing  through  the  body  of  the  animal, 
forms  a  white  calcareous  mud,  at  first  sight  not  very  unlike  chalk. 

But  the  coral  polyps  may  be  reckoned  among  the  most  important 
rock  builders  in  the  shallower  seas.  Certain  species  of  coral  live  in 
almost  all  waters,  and  range  down  to  very  considerable  depths. 
These,  however,  are  often  small,  commonly  more  or  less  isolated  in 
their  habits,  never  forming  large  colonies  or  constructing  reefs  ;  but 
the  builders  flourish  within  more  narrow  limits,  both  horizontal  and 

*  A.  Agassiz,  "  Three  Cruises  of  the  Blake"  ch.  iii. 


THE  PROLETARIAT  OF  NATURE.  189 

vertical.  They  require  pure  and  well-aerated  sea  water,  with  a  tem- 
perature ranging  from  70°  to  80°  F.  (not  falling  below  68°),  and  so  far 
as  is  at  present  known,  the  reef  builders  cannot  establish  themselves 
on  the  seabed  when  its  depth  exceeds  twenty-five  fathoms.  It  is 
true  that  in  isolated  cases  corals  of  reef-building  species  have  been 
dredged  up  from  much  greater  depths,  but  as  yet  no  instance  of  a 
growing  reef  has  been  observed  beyond  that  limit.  The  polyps 
also  cannot  endure  long  exposure  to  the  air,  so  that  the  reef  does 
not  grow  quite  up  to  the  level  of  high  water.  Hence  the  living 
polyps  have  a  vertical  range  of  about  150  feet,  and  a  reef  cannot 
exceed  this  thickness  unless  by  a  slow  subsidence  of  the  sea  bed 
space  is  obtained  for  the  formation  of  fresh  layers  of  living  corals. 

Coral  reefs  may  be  separated  into  three  groups — fringing  reefs, 
barrier  reefs,  and  atolls.  /The  first  are  attached  to  the  coast,  and  may 
completely  encircle  an  island,  being  only  interrupted  here  and  there 
where  the  embouchure  of  a  stream  renders  the  water  too  brackish  or 
too  muddy  for  the  polyps  to  exist.  The  barrier  reefs  are  at  a  dis- 
tance from  land,  sometimes  of  a  few  hundred  yards,  sometimes  of 
several  miles.  "  The  great  barrier  reef  off  the  island  of  New  Cale- 
donia extends  in  a  N.W.  and  S.E.  direction  for  a  distance  of  upward 
of  400  miles,  and  that  off  the  northeastern  coast  of  Australia  has  a 
linear  extension,  with  interruptions,  of  more  than  1000  miles.  In 
the  case  of  the  latter  the  width  of  the  intervening  strait  is  between 
50  and  60  miles,  with  a  depth  of  water  reaching  350  feet,  The  reef 
patches  themselves,  even  in  their  broader  parts,  rarely  exceed  I  or  2 
miles  in  width."* 

The  atolls  consist  of  an  irregular  ring  of  living  and  dead  coral, 
inclosing  an  expanse  of  water  called  the  lagoon,  which  usually 
communicates  with  the  open  sea  by  at  least  one  channel,  situated 
generally  upon  the  leeward  side  of  the  atoll.  In  extent  this 
"  varies  from  2  to  3  miles,  or  less :  in  length  to  upward  of  40  or  50 
miles.  Where  the  dimensions  are  very  small  the  lagcon  may 
be  completely  absent,  or  merely  indicated  by  a  dry  depression — the 
breadth  of  the  coral  ring  itself  does  not  usually  exceed  1000  to 
1500  feet,  or  somewhat  more  than  a  quarter  of  a  mile.  In  the 
general  composition  of  an  atoll  the  following  parts  may  be  recog- 
nized :  First,  an  outer  platform  of  coral-rock,  more  or  less  exposed 
at  low  water,  which  is  the  correspondent  of  the  ordinary  rock  plat- 
forms resulting  from  tidal  destruction ;  secondly,  the  beach  line 

*  Heilprin,  "  The  Bermuda  Islands,"  ch.  iv. 


tgd  THE   STORY  Of  OUR  PLANET. 

proper,  measuring  a  few  feet  in  height,  and  consisting  of  coral  sand, 
calcareous  pebbles,  and  triturated  shells ;  and  thirdly,  the  exposed 
ring  itself,  with  the  width  as  above  stated,  over  which,  more  espe- 
cially on  the  windward  side,  a  luxuriant  vegetable  growth  is  devel- 
oped. The  elevation  of  this  portion  of  the  atoll  more  commonly 
does  not  exceed  10  to  20  feet,  although  exceptionally  wind-swept 
dunes  of  coral  sand  attain  a  much  greater  height.  .  .  On  the  Ber- 
mudas they  considerably  exceed  200  feet,  reaching  at  one  point, 
Sears'  Hill,  260  feet."* 

The  relationship  of  these  three  types  of  reef  and  the  cause  of 
atoll  structure  has  been,  from  time  to  time,  a  subject  of  much  con- 
troversy. This,  after  a  period  of  comparative  repose,  again  became 
active  about  thirteen  years  since,  and  has  continued  intermittently 
to  the  present  time.  For  some  while  prior  to  the  date  named  the 
hypothesis  advanced  by  the  late  Charles  Darwin  had  held  almost 
undisputed  possession  of  the  field.  Its  main  features,  as  stated  in 
his  well-known  work  "  The  Structure  and  Distribution  of  Coral 
Reefs," f  were  as  follows:  The  first  stage  in  reef  growth  is  a  fring- 
ing reef,  and  the  variations  in  form  which  coral  reefs  exhibit  are 
mainly  due  to  subsidence  of  the  foundations  on  which  they  rest,  or, 
in  other  words,  .of  the  earth's  crust.  Suppose  a  fringing  reef  to 
have  been  established,  and  the  mass  to  be  approaching  the  surface 
of  the  sea,  the  conditions  of  growth  will  no  longer  be  equally  favor- 
able in  all  parts  of  it.  The  polyps  on  the  outer  margin  of  the  reef 
will  be  supplied  with  better  aerated  water  and  with  more  abundant 
food  than  those  nearer  to  the  land,  so  they  will  grow  more  vigor- 
ously than  the  others,  which  will  gradually  dwindle,  and  at  last 
will  die.  So  long  as  the  depth  will  permit,  the  reef  will  advance 
seaward,  and  will  be  parted  from  the  shore  by  a  narrow  and  shallow 
channel.  If  the  land  then  begins  to  sink  slowly  down,  the  reef  will 
continue  its  upward  growth,  and  the  breadth  of  this  channel  will  be 
increased,  until  the  reef,  which  originally  was  a  fringing  one,  has 
been  converted  into  a  barrier  reef.  But  when  this  is  separated  from 
the  new  coast  line  by  a  fairly  broad  interval  of  sea,  coral  polyps  can 
again  establish  themselves  in  the  neighborhood  of  the  shore,  and 
can  begin  another  fringing  reef. 

The  atoll  indicates  a  special  and  the  last  stage  in  a  process  of 
submergence.  Suppose  a  fringing  reef  to  have  been  formed  round 

*  Heilprin,  he.  cit. 

fThe  first  edition  was  published  in  1842,  the  second  in  1874,  a  third  (posthumous)  in 
1889. 


THE  PROLETARIAT  OF  NATURE.  191 

a  comparatively  low  island.  As  the  latter  is  gradually  submerged 
the  reef  continues  to  grow  upward,  but  its  growth  inward  is 
checked,  as  has  been  already  described ;  so  that,  after  a  time,  it  will 
be  separated  from  the  land,  which  is  now  greatly  reduced  in  size. 
At  last  this  disappears,  leaving  a  ring  of  growing  coral,  with  a 
lagoon  or  open  space  of  water  in  the  center.  When  the  downward 
movement  of  the  land  ceases,  the  upward  growth  of  the  coral  will 
be  arrested,  after  a  time,  by  its  proximity  to  the  surface  of  the  water. 
The  reef,  however,  can  still  continue  to  increase  in  this  direction ; 
the  waves  break  off  pieces  of  coral  from  the  sides  and  heap  them 
up  on  the  platform  together  with  debris,  chiefly  organic,  of  various 
kinds,  so  that  the  atoll  at  last  is  raised  above  water ;  seeds  are 
dropped  on  to  it  by  birds  or  washed  up  on  it  as  they  drift  about, 
and  vegetation  clothes  its  surface.  Thus  every  atoll  is  a  token  of 
subsidence  in  the  past ;  it  is  a  monument  erected  by  Nature's 
architects  over  the  grave  of  a  drowned  island. 

This  hypothesis  of  the  origin  of  coral  reefs  and  atolls  accorded  so 
well  with  most  of  the  known  facts  that  for  several  years  it  was 
generally  accepted.  But  of  late  more  than  one  observer  of  no  small 
experience  has  disputed  its  accuracy.  It  is  alleged  that  when  any 
direct  evidence  as  to  the  direction  of  motion  can  be  obtained  by 
an  examination  of  atolls  and  other  reefs,  this  intimates  upheaval, 
not  subsidence,  as  masses  of  dead  coral  can  be  found  elevated, 
sometimes  to  a  very  considerable  height,  above  the  sea  level. 
Examination  of  the  reefs  thus  laid  bare  indicates  that  marine 
organisms,  other  than  corals,  play  an  important  part  in  preparing 
the  foundations  of  the  reef,  and  that  this  does  not  attain  to  the 
thickness  which  might  have  been  expected  had  it  been  formed  by 
long-continued  subsidence.  It  is  also  noticed  that  all,  or  almost  all, 
the  smaller  oceanic  islands,  if  not  atolls,  are  of  .volcanic  origin ;  if 
this  be  so,  it  is  not  necessary  to  appeal  to  subsidence  in  order  to 
account  for  the  existence  of  a  shoal  in  the  open  ocean,  fpr  it  may 
be  either  the  top  of  a  volcanic  mass  which  has  never  reached  the 
surface  or  the  remains  of  one,  like  Graham  Island  in  the  Mediter- 
ranean, the  looser  materials  of  which  have  been  washed  away  by 
the  waves.  In  cases  where  the  summit  of  the  volcanic  mass  lay  too 
deep  below  the  surface  of  the  sea  to  permit  of  the  reef  builders 
establishing  themselves,  this,  in  course  of  time,  might  be  brought 
within  the  requisite  distance  (about  twenty-five  fathoms)  by  the 
accumulation  of  other  organisms,  such  as  mollusca,  foraminifera,  etc. 
This  would  not  be  difficult,  for  every  layer  of  sea  water  one  hundred 


192  THE    STORY  OF  OUR   PLANET, 

fathoms  deep  and  a  mile  square  contains  more  than  sixteen  tons  of 
carbonate  of  lime,  which  can  be  abstracted  by  marine  organisms, 
and  will  amply  suffice  for  building  up  a  substratum  for  the  reef. 
The  ring-like  form  was  thus  explained  :  At  first  the  top  of  the 
buried  shoal  would  be  covered  by  a  cake-like  mass  of  the  coral 
polyps ;  but  as  this  grew  upward  it  would  assume  a  ring-like  form, 
since  toward  the  outside  the  polyps,  as  already  explained,  would  be 
more  vigorous  than  those  within.  The  ring  also  would  tend  to 
spread  outward,  for  all  round  it  a  talus  of  broken  coral  and  dead 
mollusks  would.be  formed,  on  which,  as  a  foundation,  the  reef  might 
continue  to  grow.  Thus  it  would  not  only  assume  a  more  or  less 
circular  form,  but  also  expand  in  process  of  time  like  a  fairy  ring. 
This  method  of  growth  would  originate  a  lagoon,  which  also  might 
be  enlarged  ;  for  after  a  time  its  semi-stagnant  waters  would  be 
unfavorable  to  coral  life.  Its  sides  and  bed  would  be  covered  with 
dead  coral — this  would  be  dissolved  by  the  sea  water — and  the  car- 
bonate of  lime  would  be  borne  away  by  the  ebbing  tide  and  once 
more  restored  to  the  ocean  from  which  it  had  been  borrowed. 

The  new  hypothesis,  however,  is  itself  open  to  criticism.  For 
instance,  the  objection  to  the  theory  of  subsidence,  that  coral 
islands  commonly  testify  to  upheaval,  is  less  weighty  than  it  seems. 
No  one  hesitates  to  admit,  as  will  be  indicated  in  a  later  chapter, 
that  the  western  coasts  of  Norway  and  of  Britain  have  been  very 
considerably  depressed  since  the  existing  contours  of  the  land  were 
sculptured,  yet  the  latest  movements  no  less  certainly  have  been  in 
an  upward  direction.  It  may  be  admitted  that  foraminifera  and 
other  lime-secreting  organisms  accumulate  on  the  bed  of  the  sea; 
but  it  may  be  doubted  whether  these,  except  under  special  circum- 
stances, such  as  may  be  found  on  the  Florida  coast  (which  cannot 
be  extended  to  the  open  ocean),  will  contribute  materially  to  the 
work  of  bringing  a  submarine  shoal  up  to  the  right  distance  from 
the  surface.  Sixteen  tons  of  carbonate  of  lime  sounds  like  a  very 
large  quantity ;  but  what  does  it  represent  when  regarded  in  the 
cold  light  of  an  arithmetical  calculation?  If  precipitated  from  the 
sea  water  over  a  surface  of  the  same  area  (a  mile  square),  it  would 
produce  a  solid  layer  rather  less  than  .0001  of  an  inch  in  thickness. 
Even  if  it  be  built  up  in  the  form  of  hollow  organisms,  such  as 
globigerina,  and  these  be  piled  lightly  one  on  another,  the  layer 
could  not,  on  the  most  liberal  estimate,  reach  a  tenth  of  an  inch. 
Contributions  from  this  source  to  the  task  of  elevating  the  surface 
of  a  submarine  hill  could  not  be  very  important.  Professor  Heil- 


THE  PROLETARIAT  OF  NATURE. 


193 


prin,  regarding  the  problem  from  another  point  of  view,  estimates 
that  the  annual  accumulation  could  not  exceed  7oVo  Pai"t  of  an 
inch — that  is  to  say,  a  period  of  about  one  hundred  thousand  years 
would  be  required  to  build  up  a  layer  only  one  foot  in  thickness.* 
If  a  shoal  covered  by  a  hundred  fathoms  of  water  is  to  be  brought 
up  to  the  lower  limit  of  reef-coral  life,  an  accumulation  of  organisms 
seventy-five  fathoms  thick  is  needed,  and  this  would  require  forty- 


>'•**.. 


Sketch  of  Masamarhu  I. 

showing  approximate 
position  of  Se 


FIG.  78. — MASAMARHU  ISLAND.     MAP  AND  SECTION  II. 

five  million  years.  The  test  may  be  too  severe,  and  the  result  may 
somewhat  overstate  the  difficulty,  but  it  seems  certain  that  these 
small  organisms  must  accumulate  so  slowly  that  only  very  rarely 
can  an  appeal  be  made  to  such  a  method  of  laying  the  foundation 
for  a  coral  reef  in  the  open  ocean.  The  white  chalk  beneath  Lon- 
don, which  consists  mainly  of  organic  material,  is  commonly  about 
fifty  fathoms  thick,  and  the  total  thickness  of  the  whole  mass  of 
chalk  is  not  very  much  more  than  double  this  amount,  so  that  the 
quantity  of  organic  material  demanded  for  laying  the  foundations 
of  a  reef  at  a  depth  of  a  hundred  fathoms  would  be  not  very  much 
less  than  that  which  is  contained  in  the  whole  chalk,  white  and  gray. 
Nature's  work  is  usually  slow  as  man  counts  time,  but  we  may 
reasonably  feel  doubts  whether  it  is  conducted  in  such  a  very 


"  The  Hermuda  Islands,"  ch.  iv. 


194 


THE   STORY  OF  OUR  PLANET. 


leisurely  manner  as  this.  The  method  proposed  for  the  enlarge- 
ment of  lagoons  by  the  corrosive  action  of  sea  water  on  dead  coral 
also  presents  serious  difficulties.  It  is  undoubtedly  true,  as  already 
stated,  that  calcareous  organisms,  under  certain  circumstances,  are 
dissolved  in  the  ocean.  But  what  are  these  circumstances  ?  Cor- 
rosion takes  place  when  the  material  is  at  a  depth  in  the  ocean  of 
some  two  thousand  fathoms — in  other  words,  when  it  is  exposed  to 


ZOnO 


FIG.  79. — MASAMARHU  ISLAND.     SECTION  I. 


a  pressure  equivalent  to  that  of  four  hundred  atmospheres,  or  about 
five  thousand  six  hundred  pounds  on  the  square  inch.  In  shallow 
water,  as  is  proved  by  the  existence  and  accumulation  of  the  fora- 
miniferal  ooze,  the  corrosive  action  is  so  slight  as  to  be  unimportant, 
though  probably  it  would  become  somewhat  greater  in  the  actual 
wash  of  the  waves  and  in  the  changing  circumstances  of  tidal  water; 
but  these  abyssal  conditions,  as  is  well  known,  present  no  analogies 
with  the  case  under  consideration,  and  cannot  be  introduced  into 
the  question.  This  argument,  indeed,  and  the  last,  appear  to  be 
mutually  destructive,  for  if  water  has  such  solvent  action,  how 
could  organisms  construct  the  foundation  of  a  reef?  Moreover, 
the  dead  coral  of  reefs  rather  rapidly  takes  up  magnesia  from  sea 
water,  and  is  thus  converted  into  dolomite — a  process  to  which  the 
conditions  within  a  lagoon  would  be  exceptionally  favorable.  So 


THE  PROLETARIAT  OF  NATURE.  195 

that,  as  this  salt  is  less  soluble  than  ordinary  carbonate  of  lime,  any 
material  enlargement  of  a  lagoon  by  the  corrosive  action  of  sea 
water  does  not  seem  probable. 

It  is  quite  true  that  some  reefs  are  thin,  but  others  rise  so  rapidly 
from  depths  much  exceeding  25  fathoms  that,  so  far  as  at  present 
known,  we  are  driven  to  suppose  that  either  the  reef  has  been 
continuously  subsiding  for  a  long  time,  since  it  first  began  to  grow, 
or  the  reef  builders  can  flourish  at  depths  not  less  than  from  100  to 
200  fathoms.  In  favor  of  the  latter  supposition  no  valid  evidence  has 
been  yet  adduced,  and  25  fathoms,  as  already  said,  has  been  adopted 
almost  unanimously  by  all  those  who  have  studied  the  question  of 
the  lower  limit  of  reef-building  corals.  Unless,  then,  some  other 
alternative  can  be  devised,  such  reefs  as  Masamarhu  Island,  in  the 
Red  Sea,  indicate  a  region  of  subsidence  (Figs.  78,  79).  No  attempt 
has  yet  been  made — for  it  would  be  a  difficult  and  expensive  opera- 
tion— to  determine  the  depth  of  a  coral  reef  by  boring,  but  the 
evidence  obtained  in  making  some  wells  in  Oahu  (one  of  the  Sand- 
wich Islands),  so  far  as  it  goes,  is  favorable  to  the  hypothesis  of 
subsidence.  During  these  borings  coral  rock  was  pierced  at  various 
depths  below  150  feet,  down  to  1048  feet,  and  in  one  case  a  mass 
of  "  hard  coral  rock,  like  marble,"  was  struck  at  depths  of  320  feet, 
and  proved  to  be  505  feet  thick.  As  the  cores,  so  far  as  is  stated, 
were  not  examined  by  an  experienced  geologist,  some  doubt  may 
be  felt  as  to  the  accuracy  of  the  identification ;  still  it  is  difficult  to 
understand  how  such  a  phrase  could  be  applied  to  anything  but  a 
semi-fossil  reef.  If  this  be  correct,  either  there  has  been  consider- 
able subsidence  or  the  reef  not  only  began,  but  also  ceased  to 
grow,  at  a  greater  depth  than  25  fathoms,  and,  further,  it  attained  a 
thickness  of  more  than  triple  this  amount. 

But  whatever  may  be  the  conclusion  which  is  ultimately  adopted 
as  to  the  genesis  and  history  of  a  coral  reef— a  subject  which  very 
probably  may  prove  to  be  more  varied  and  complicated  tharj  at  first 
was  supposed  * — the  fact  is  indisputable  that  these  polyps,  at  the 
present  day,  contribute  largely  in  certain  regions  of  the  globe  to  the 
formation  of  limestones.  In  this  task  they  have  taken  an  impor- 
tant part  since  a  very  early  period  in  geological  history.  Corals, 
even  in  cases  to  which  we  might  hesitate  to  apply  the  term 
reef,  are  abundant  among  the  mollusks,  polyzoa,  crinoids,  and  other 
echinoderms,  which  can  be  readily  recognized  in  blocks  of  fossil 

*A  summary  of  the  different  opinions  and  arguments  is  given  in  Darwin's  "Coral 
Reefs,"  Appendix  II.,  third  edition. 


196 


THE   STORY  OF   OUR  PLANET. 


limestone,  and  fragments  of  them  may  be  identified  among  those 
of  the  other  organisms  which,  with  foraminifera  and  algae,  make 
up  the  interstitial  material  of  the  rock.  Reef  builders,  however, 

were  certainly  at  work  in  the  sea 
which  covered  Shropshire  in  Silurian 
ages,  Devonshire  in  Devonian,  and 
Gloucestershire  in  Jurassic,  though 
in  the  British  Isles  the  conditions 
appear  to  have  been  less  favorable, 
on  the  whole,  to  their  development 
than  they  were  in  some  other  re- 
gions, still  even  here  corals  are 
often  abundant  in  limestones.  The 
gray  limestone  of  Derbyshire  may  be 
often  seen  to  be  crowded  either  with  large  bivalve  shells,  packed  as  in 
a  modern  oyster  bed,  or  with  the  broken  stems  of  crinoids,  close  as 
sticks  in  a  heap  (Fig.  80).  The  oolitic  limestones  of  Somersetshire 
and  Gloucestershire,  of  Rutlandshire  or  Lincolnshire,  of  many 
localities  from  Dorsetshire  to  Yorkshire,  are  accumulations  of  organ- 
isms, often  pounded  into  sand  by  the  waves,  no  less  than  the  rock 
which  is  still  in  process  of  formation  on  the  shores  of  Ascension  or 
of  the  Sandwich  Isles.  Thus  the  very  dust  has  been  once  alive, 
and  the  chief  ministrants  to  the  comfort,  the  prosperity,  and  the 
civilization  of  man  have  been  the  humbler  members  of  that  living 
world  at  the  head  of  which  he  claims  to  stand. 


FIG.  80. — LIMESTONE  WITH 
CRINOID  STEMS. 


FIG.  81.— NUMMUUTIC  LIMESTONE. 


PART  III. 
CHANGES   FROM   WITHIN. 


CHAPTER  I. 

MOVEMENTS   OF   THE   CRUST. 

THE  surface  of  the  earth's  crust,  as  we  have  endeavored  to  show 
in  the  preceding  chapters,  is  never  at  rest ;  from  the  topmost  crags 
of  the  loftiest  mountain  peaks  to  the  deepest  abyss  in  the  ocean 
floor,  the  work  of  destruction,  of  transference,  of  deposition  is  con- 
stantly carried  on ;  the  debris  worn  by  the  waves,  the  torrent,  or  the 
glacier,  or  that  swept  along  by  the  current,  comes  to  rest  at  last ; 
mineral  substances,  after  vanishing  for  a  time  by  solution  in  water, 
whether  of  river  or  sea,  are  again  made  visible  by  life's  magic  force, 
enter  for  a  time  its  service,  then  drop  back  once  more  into  the  inor- 
ganic world,  and  are  incorporated  again  into  masses  of  rock.  The 
constituents  of  the  crust  are  ever  entering  into  new  combinations; 
the  surface  rises  and  falls,  as  if  it  were  the  breast  of  some  huge 
monster,  slowly  breathing  as  it  sleeps,  or  quivers  as  if  from  the  pul- 
sations of  a  hidden  heart.  The  rock  which  now  crowns  some  tow- 
ering peak  was  built  up  grain  by  grain  in  the  ocean  depths.  The 
alluvium  of  ancient  rivers,  the  soil  of  vanished  forests,  the  debris  of 
old  land  surfaces,  may  be  pierced  in  the  deepest  mines,  far  beneath 
the  present  ocean  level.  Ages  before  the  first  stone  was  laid  in  the 
walls  of  London  another  and  a  greater  Thames  swept  eastward  to 
the  sea.  The  shelving  valley  bed,  now  so  thickly  studded  with 
houses,  is  excavated  in  a  tenacious  mud  such  as  is  still  in  process  of 
formation  off  the  mouth  of  the  Ganges  or  of  the  Nile.  The  higher 
hills  which  at  present  bound  the  valley  on  either  side  were  once 
built  up  by  a  rain  of  dead  organisms  on  the  ocean  floor,  like  the 
ooze  which  is  collecting  deep  down  beneath  the  surface  of,the  open 
Atlantic.  The  poet  uttered  no  dreamer's  words,  but  simple  scien- 
tific truth,  when  he  declared  : 

There  rolls  the  deep  where  grew  the  tree. 

O  Earth,  what  changes  hast  thou  seen ! 

There  where  the  long  street  roars  hath  been 
The  stillness  of  the  central  sea. 

Evidence  of  these  changes  of  level  can  be  sometimes  obtained  from 
history  or  from  tradition ;  more  often  they  must  be  inferred  from 


200  THE   STORY  OF  OUR  PLANET. 

the  handwriting  of  Nature,  the  characters  graven  on  the  rocks.  Of 
the  former — the  historical  evidence — a  few  examples  may  suffice. 
The  first,  and  on  the  whole  the  most  complete — for  it  is  an  instance 
of  both  subsidence  and  upheaval,  and  the  whole  episode  extended 
over  a  period  which  hardly  exceeded  fourteen  centuries — must  be 


FIG.  82. — COLUMNS  IN  THE  "TEMPLE  OF  SERAPIS." 


briefly  recapitulated,  though  it  has  been  often  quoted.  West  of  the 
headland  on  which  stands  Pozzuoli,  the  ancient  Puteoli,  is  a  narrow 
plain,  barely  above  sea  level,  which  intervenes  between  the  water 
and  the  base  of  an  inland  cliff.  Of  itself  this  is  enough  to  suggest 
that  the  water  formerly  reached  a  higher  limit,  but  is  insufficient  to 
give  any  definite  date  to  either  submergence  or  elevation.  About 
a  quarter  of  a  mile  from  the  town  three  columns  of  Cipollino 
marble,  rather  more  than  forty  feet  high,  rise  above  the  plain.  In 


MOVEMENTS  OF   THE   CRUST.  201 

the  earlier  part  of  the  last  century  only  about  three-quarters  of  each 
column  stood  above  ground,  but  in  the  year  1750  the  site  was 
excavated,  and,  at  a  depth  of  about  ten  feet  from  the  surface,  a 
pavement  was  reached,  the  ruins  of  which  were  uncovered.  It  was 
discovered  that  these  columns  had  formed  part  of  a  considerable 
building ;  portions  of  the  other  columns,  some  of  granite,  some  of 
various  marbles,  lay  broken  on  the  marble  pavement.  Some  sculp- 
tured work  and  inscriptions  were  also  found.  Commonly  this  build- 
ing is  called  the  Temple  of  Serapis,  but  the  accuracy  of  the  name  is 
disputed.  That  question,  however,  may  be  left  to  antiquarians; 
for  geologists  the  ruins  have  other  interests.  It  was  observed,  and 
the  marks  are  still  as  clear  as  ever,  that  the  shafts  of  these  three 
columns  were  thickly  pierced  with  roundish  holes  all  over  a  band 
extending  from  ten  up  to  eighteen  feet  from  the  floor.  These 
exactly  resemble  the  deep  cavities  made  in  rocks  and  stones  by  a 
mollusk  (Modiola  lithophagd]  which  is  still  abundant  in  the  Mediter- 
ranean. Above  this  pitted  zone  the  marble  was  smooth,  and  it  so 
continued  for  the  remainder  of  the  shaft — about  twenty-four  feet.* 
At  that  time  the  dead  shells  of  this  bivalve  and  one  or  two  other 
mollusks  still  remained  in  the  burrows.  Some  of  the  broken  marble 
columns  which  lie  on  the  pavement  are  pierced  in  like  fashion.  In 
these,  however,  the  holes  do  not  extend  all  round  the  shaft,  but 
cover  only  one  side  of  it,  and  are  sometimes  sunk  in  the  broken 
ends,  so  that  when  they  were  made  the  column  was  fractured  and 
prostrate.  Thus  the  evidence  which  the  building  itself  supplies 
leads  irresistibly  to  the  conclusion  that  after  it  had  become  ruinous, 
and  rubbish  had  accumulated  around  the  bases  of  these  three  col- 
umns, the  ground  sank  to  a  depth  of  at  least  twenty  feet  below  its 
former  level,f  and  the  pillars  must  have  been  partly  immersed  in 
the  sea  long  enough  to  allow  the  mollusks  to  burrow  into  the  stone  ; 
then  they  were  uplifted  to  something  like  their  original  position. 

What  light,  then,  is  thrown  by  history  on  these  singular  changes  ? 
Its  testimony  is  not  very  full,  but  it  is,  fortunately,  sufficient  to 
render  the  geological  story  much  more  precise.  Inscriptions  dis- 
covered in  the  "temple"  show  that  it  was  restored  (to  use  the 
modern  phrase)  by  Septimius  Severus,  and  afterward  by  Alexander 


*  The  height  of  the  shafts  is  about  forty-two  feet. — Phillips,  "  Vesuvius,"  ch.  viii. 

\  The  top  of  the  perforated  zone,  according  to  Professor  Phillips,  in  1879  was  about 
sixteen  feet  above  high  water  mark  ;  when  the  excavations  were  made  the  height,  as  will 
be  further  explained,  was  somewhat  greater. 


202  THE  STORY  OF  OUR  PLANET. 

Severus.*  As  on  each  occasion  an  enrichment  with  precious  mar- 
bles is  mentioned,  it  may  be  safely  assumed  that  before  the  year 
235  these  columns  had  been  placed  in  the  building.  For  several 
centuries  after  this  date  no  direct  testimony  can  be  found  as  to  the 
fate  of  the  structure,  but  much  is  indirectly  told.  In  the  year  410 
Pozzuoli  was  sacked  by  Alaric  the  Goth ;  in  44$  it  suffered  the  same 
fate  from  Genseric  the  Vandal.  These  invaders — like  all  barbarians, 
whether  in  the  fifth  or  the  nineteenth  century — destroyed  from 
mere  wantonness,  so  that  if  the  "  temple  "  by  some  fortunate  chance 
had  escaped  the  Goth,  it  is  almost  certain  to  have  been  ruined  by 
the  Vandal.  An  age  when  empires  are  tottering  to  their  fall  is  not 


FIG.  83.— THE  TEMPLE  OF  SERAPIS,  AT  THE  TIME  OF  DEEPEST  SUBMERGENCE. 

The  four  deposits  described  in  the  text  are  indicated  within  the  walls  of  the  building. 

one  for  the  restoration  of  ancient  monuments,  so  it  may  be  safely 
assumed  that  as  the  building  was  left  by  the  Vandal  so  it  remained. 
For  nearly  eleven  centuries  nothing  more  of  it  is  known;  then  an 
author  named  Loffredo  states  that  fifty  years  before  the  date  when 
he  wrote  (1580)  the  sea  washed  the  base  of  the  cliff  already  men- 
tioned, so  that  it  was  possible  to  fish  from  certain  ruins  at  its  top. 
From  this  it  follows  that  about  the  year  1530  the  pillars  must  have 
been  standing  in  the  sea.  The  land,  however,  had  already  begun  to 
rise,  for  in  1503  Ferdinand  and  Isabella  granted  to  the  city  and 
university  of  Pozzuoli  some  land  "  where  the  sea  is  drying  up,"  and 
again  in  1511  some  more  land  where  "  the  sea  has  dried  up."  Again, 
we  read  that  in  1538,  at  the  time  of  the  eruption  by  which  Monte 
Nuovo  was  formed,  half  a  league  away,  at  the  other  end  of  this  low- 
land strip,  "  the  seashore  was  dried  up  about  Pozzuoli  and  Baiae, 
showing,  among  other  things,  newly  discovered  ruins."  Two  grants 
of  new  land  in  less  than  ten  years  seem  to  indicate  that  the  rise 
was  comparatively  rapid,  and  the  whole  change  may  have  been 
brought  about  in  less  than,  a  century,  but  nothing  further  is  known 
either  on  this  point  or  as  to  the  manner  of  the  subsidence.  An 

*  The  former  reigned  A.  I).  193-211,  the  latter  222-235. 


MOVEMENTS  OF   THE   CRUST.  203 

eruption  of  the  Solfatara,  a  crater  rather  more  than  a  mile  away  to 
the  northeast,  occurred  in  1198,  and  a  severe  earthquake  in  1488, 
but  neither  of  these  can  be  connected  with  the  submergence  by  any 
direct  evidence.*  The  rubbish  which  protected  the  lower  part  of 
the  columns  indicates,  on  the  whole,  that  some  time  must  have 
elapsed  after  the  building  became  a  ruin  before  it  sank  deep 
enough  to  be  attacked  by  the  boring  mollusks.  The  floor  was  cov- 
ered by  a  dark  tufaceous  deposit,  about  two  feet  thick,  which, 
however,  contained  some  serpulae.  This  indicates  that  the  sea  had 
obtained  access  to  the  floor  of  the  temple,  and  mingled  its  waters 
with  those  of  the  calcareous  spring.  For  a  time,  then,  the  depres- 
sion must  have  been  only  a  slight  one.  Over  this  bed  lay  an  irregu- 
lar mass  of  volcanic  ash,  with  an  uneven  surface  from  five  to  nearly 
nine  feet  above  the  pavement.  This,  however,  was  probably  thrown 
down  in  a  few  hours,  or,  at  most,  days ;  it  may  have  been  ejected 
from  the  Solfatara  in  the  twelfth  century.  A  mass  of  calcareous 
tufa  covered  these  ashes,  filling  up  the  hollows,  its  even  top  being 
nine  feet  from  the  floor.  To  form  this  the  waters  of  the  spring 
already  mentioned  must  have  been  obstructed  by  the  volcanic  rub- 
bish, and  a  pool  formed.  As  precipitation  of  tufa  would  not  take 
place  in  the  sea,  the  deposit  indicates  that  up  to  this  time  the  level 
of  the  land  had  but  slightly  fallen.  The  tufa  was  covered  by  about 
a  couple  of  feet  of  ashy  material,  such  as  might  have  fallen  in  a 
second  eruption,  or  have  been  washed  in  by  the  sea  when  it  first 
obtained  access;  and  above  that  the  burrows  began.  If  the  irregu- 
lar mass  of  volcanic  ash  is  rightly  referred  to  the  eruption  of  the 
Solfatara,  this  leaves  about  three  centuries  only  for  the  precipitation 
of  the  tufa,  the  submergence  to  a  depth  of  nine  or  ten  feet  above  it, 
and  the  excavation  of  the  burrows  in  the  marble.  If  so,  as  the  first 

*  A  letter  from  Mr.  J.  E.  H.  Thomson,  published  in  the  Geological  Magazine,  1892^ 
p.  282,  draws  attention  to  a  passage  in  the  Ada  Petri  et  Patili  which  at  first  sight  seems 
to  help  in  fixing  the  date  of  the  submergence.  This  states  that  Puteoli  sank  inlo  the  water 
when  St.  Paul  prayed  it  might  be  punished  for  the  martyrdom  of  Dioscurus.  From  this 
Mr.  Thomson  argues  that  when  the  book  was  written  the  place  must  have  been  long  under 
water  (i.  e.,  in  the  fifth  century,  the  date  assigned  to  the  Acta).  So  he  suggests  that  the 
submergence  probably  occurred  ' '  between  the  middle  of  the  third  century  and  the  middle 
of  the  fourth."  But  the  evidence,  in  my  opinion,  is  not  worth  much.  The  book  is  com- 
posite and  of  various  dates,  parts  being  much  older  than  the  above  era  ;  it  is  also  of  East- 
ern, not  of  Western  origin,  so  that  little  confidence  can  be  placed  in  the  "  local  coloring," 
or  in  any  geographical  information.  The  tradition  may  be  founded  on  nothing  better  than 
the  fact  that  in  the  Bay  of  Baioe  the  foundations  of  houses  were  often  laid  in  the  sea  itself, 
which  might  give  rise  in  process  of  time  to  the  notion  that  the  land  had  sunk.  (See  Horace, 
"Odes,"  iii.  i,  33-37.) 


204  THE   STORY  OF  OUR  PLANET. 

and  last  would  occupy  some  time,  the  downward  movement  must 
have  been  fairly  rapid. 

This,  however,  is  not  all :  at  a  depth  of  about  five  feet  the  floor  of 
an  older  building  was  discovered.  So,  beneath  the  pavement  of  the 
present  ruins — that  is,  well  below  high  water  mark — there  is  prob- 
ably a  record  of  some  earlier  change  of  level ;  but  in  any  case  the 
land  has  not  remained  at  rest  since  1750.  When  the  excavation 
was  completed,  the  pavement  of  the  ruin  was  above  high  water 
mark.  Gradually  the  sea  obtained  access  to  it,  and  about  half  a 
century  since  the  rate  of  subsidence  was  estimated  at  an  inch  in 
four  years.*  It  is  believed  that  the  movement  has  now  ceased,  but 
it  had  been  carried  so  far  that  a  few  years  since  a  new  floor  had  to 
be  constructed,  so  as  to  raise  the  level  by  about  two  feet,  as  the  old 
pavement  was  under  water.  In  other  parts  of  the  Bay  of  Baiae  evi- 
dence of  subsidence  since  Roman  times  has  been  discovered,  so  that 
these  movements  have  affected  a  considerable  tract  of  country, 
though  not  necessarily  to  the  same  extent. 

This  region,  however,  is  a  volcanic  one,  where  disturbances  of  the 
earth's  crust  might  be  expected,  in  which  also  they  might  well  be 
comparatively  local,  so  that  other  examples  must  be  sought  in  dis- 
tricts under  more  normal  conditions.  Several  instances  of  changes 
in  level,  both  upward  and  downward,  are  on  record,  but  these  more 
commonly  are  associated  with  earthquakes.  For  instance,  in  New 
Zealand  the  ground  has  been  upraised  more  than  once.  A  small 
cove  about  eighty  miles  north  of  Dusky  Bay,  which  formed  an 
excellent  harbor  for  boats  and  had  been  long  used  by  the  natives, 
was  practically  converted  into  dry  land  after  the  earthquakes  of 
1826  and  the  following  year.  Still  more  remarkable  are  the  ac- 
counts of  the  changes  which  were  produced  by  the  earthquake  of 
1855,  for  it  was  estimated  that  a  district  as  large  as  Yorkshire  had 
been  elevated  from  one  to  nine  feet  above  its  former  level.  Similar 
effects  also  have  been  produced  on  the  coast  of  Chili,  while  in  the 
year  1819  by  a  movement  in  the  contrary  direction  a  tract  of  land 
in  the  Runn  of  Cutch  measuring  about  two  thousand  square  miles 
was  converted  in  a  few  hours  into  a  lagoon.  Simultaneously  with 
this  depression  a  neighboring  area  of  marshy  land  about  fifty  miles 
in  length  was  uplifted,  and  still  forms  a  low  mound. 

A  comparison    of   historical   evidence  and    the    examination  of 

*The  estimate  was  made  between  1822  and  1838. — Lyell,  "Principles  of  Geology," 
ch.  xxx. 


MOVEMENTS  OF   THE   CRUST.  205 

various  landmarks  sometimes  show  that,  in  not  a  few  regions, 
movements  of  the  land  have  occurred  quite  unaccompanied  by 
earthquakes,  and  so  slow  as  to  be  imperceptible  to  ordinary  ob- 
servation. For  instance,  the  Baltic  coast  in  the  North  of  Sweden 
has  slowly  risen  during  the  last  century,  while  at  the  southern  end 
of  the  peninsula  it  has  about  as  slowly  sunk.  In  a  little  more  than 
the  same  time  Malmo,  in  the  extreme  south,  is  believed  to  have 
subsided  about  five  feet.  This  subsidence  is  by  no  means  restricted 
to  the  South  of  Scandinavia ;  within  the  period  covered  by  history 
it  appears  to  have  affected  the  coasts  of  Schleswig,  of  Holland,  and 


FIG.  84.— TERRACES  CUT  BY  THE  SEA,  MALANGER  FJORD,  NORWAY. 

even  of  Northern  France.  A  slow  downward  movement — slight,  but 
not  inconsiderable — seems  to  have  affected  the  coast  round  the 
head  of  the  Adriatic,  at  any  rate  during  the  last  fourteen  or  fifteen 
centuries  ;  the  coast  of  Greenland  also,  from  the  sixtieth  to  the 
sixty-ninth  parallel,  has  been  slowly  settling  down.  The  native 
avoids  building  his  hut  near  to  the  water's  edge ;  the  Moravian 
missionaries  have  been  compelled  to  move  the  posts  to  which  their 
boats  are  moored  further  inland.*  But  here,  as  in  Scandinavia,  the 
motion  further  north  is  in  the  opposite  direction.  An  upward 
movement,  indeed,  seems  to  have  affected  a  very  large  area  in  the 
northern  hemisphere.  In  Siberia,  Nova  Zembla,  Franz  Joseph 
Land,  Northern  Greenland,f  raised  beaches  are  common,  and 


*  Lyell,  "  Principles  of  Geology,"  ch.  xxxi. 

f  Payer,  "  New  Lands  within  the  Arctic  Circle,"  vol.  ii.  pp.  86,  273. 


206 


THE   STORY  OF  OUR  PLANET. 


marine  organisms,  still  in  a  comparatively  fresh  condition,  have 
been  found  some  distance  inland,  and  many  feet  above  sea  level. 
At  Port  Kennedy,  near  latitude  81°  N.,  the  bone  of  a  whale  lay  on 
the  mossy  earth  164  feet  above  sea  level,  and  shells  were  found 
nearly  400  feet  higher.* 

If  account  be  taken  of  less  direct  testimony,  there  can  be  no 
question  that  very  important  changes  of  level  have  taken  place 
since  a  time,  geologically  speaking,  so  recent  that  the  physical 
features  of  the  country  have  been  in  other  respects  little  altered. 
At  Kured,  near  Uddevalla,  in  Sweden,  a  deposit  of  seashells, 


FIG.  85. — SEA-CUT  GROOVES  IN  SMOOTHED  ROCK,  N.  OF  ALTEN  FJORD,  NORWAY. 

consisting  wholly  of  living  species,  may  be  found,  together  with 
barnacles  and  corallines  still  adherent  to  the  rock.  Similar  deposits 
occur  here  and  there  along  the  Norway  coast,  while  the  raised 
beaches  already  mentioned  are  often  seen  from  one  to  two  hundred 
feet  above  sea  level,  and  may  be  traced  sometimes  to  at  least  five 
hundred  feet.  Other  proofs  of  marine  action,  such  as  wave  marks, 
may  often  be  found.  In  Nova  Zembla  these  terraces  exist  at  an 
elevation  of  at  least  six  hundred  feet,  and  on  the  Fraser  River  to 
something  like  double  this  amount.  In  several  parts  of  the  western 
coasts  of  South  America  proofs  of  a  general  rising  of  the  land  are 
clear  and  frequent,  and  in  the  neighborhood  of  Valparaiso  more 
than  one  line  of  terraces  exists,  the  highest  being  as  much  as  1295 
feet  above  the  sea. 

*Many  instances  are  cited  by  Reclus,  "  The  Earth,"  ch.  Ixxx. 


MOVEMENTS  OF    THE    CRUST.  207 

The  coasts  of  the  British  Isles  also  indicate  an  upward  move- 
ment, which  is  more  marked  in  the  north  than  in  the  south.  In 
the  latter,  however,  raised  beaches  may  be  found,  especially  in  the 
west ;  but  on  the  Scotch  coasts  terraces,  old  sea  cliffs  and  caves, 
sandy  flats  or  rocky  platforms  a  few  feet  above  sea  level,  carses,  or 
the  elevated  deltas  of  rivers,  are  to  be  found  in  numbers  of  places. 
In  the  carse  of  the  Clyde,  below  Glasgow,  several  canoes,  belonging 
to  the  age  when  tools  and  weapons  of  polished  stone  were  in  general 
use,  have  been  dug  up.  These  were  lying  some  feet  above  high 
water  mark,  and  the  general  altitude  of  the  last  and  best  preserved 
of  the  beaches  indicates  a  change  of  level  which  varies  from  twenty 
to  thirty  feet  in  the  central  valley  of  Scotland.  Similar  indications 
of  a  rise  of  land  are  to  be  found  in  Ireland,  especially  in  the  more 
northern  part ;  but  it  may  be  remarked  that  many  of  the  above- 
mentioned  districts  also  testify  that  this  uprising  is  only  a  partial 
undoing  of  a  preceding  movement  of  depression  on  a  yet  greater 
scale. 

Some  authors  have  suggested  that  the  sea,  rather  than  the  land, 
may  change  its  level,  for  its  height  must  depend  upon  the  quantity 
of  water  in  the  ocean ;  the  level  of  that  also  may  not  be  the  same 
at  all  places — in  other  words,  its  surface,  instead  of  forming  part  of 
a  sphereoidal  shell,  interrupted  only  by  the  prominences  of  islands 
and  continents,  may  be  varied  by  slight  depressions  and  elevations. 
To  some  extent  this  is  true,  for  differences  in  atmospheric  pressure 
and  winds  produce  an  effect  on  the  level  of  the  surface,  but  this  is 
unimportant.  It  is  suggested  that  larger  variations  are  possible. 
Suppose,  for  instance,  that  the  climate,  either  over  the  whole  globe 
or  in  one  of  its  hemispheres,  north  and  south  of  the  equator,  be- 
came much  colder — and  this  actually  did  happen  in  an  epoch,  geo- 
logically speaking,  not  at  all  remote — then  there  would  be  less  rain 
and  more  snow,  and  a  larger  amount  of  water  would  be  converted 
into  ice.  Thus  the  height  of  the  ocean  would  be  lowered^  because 
a  considerable  quantity  of  its  water  would  be  temporarily  added, 
in  the  form  of  ice,  to  the  solid  crust  of  the  earth.  Again,  if  in  either 
hemisphere,  in  consequence  of  this  change  of  temperature,  a  great 
ice  cap  had  been  formed  in  circumpolar  regions,  the  center  of 
gravity  of  the  globe  would  be  no  longer  at  the  center  of  the 
sphere  or  spheroid,  but  it  would  be  slightly  displaced  along  the  axis 
of  rotation  in  the  direction  of  the  cap.  But  by  this  displacement  of 
the  center  of  attraction  the  form  of  the  surface  of  the  ocean  must 
be  affected,  for  its  waters  must  assume  a  new  position  and  be 


2o8  THE   STORY  OF  OUR  PLANET. 

slightly  moved  in  the  direction  of  the  pole.  If  the  cap  be  in  the 
North  Polar  area,  the  sea,  in  consequence  of  this  change  of  form  in 
the  watery  envelope,  will  stand  at  a  higher  level  in  northern  regions 
than  was  formerly  the  case,  and  the  difference  will  become  greater 
in  proceeding  toward  this  pole.  Of  course  it  will  be  correspondingly 
lowered  in  the  southern  hemisphere.  Continental  lands  and  moun- 
tain masses  also  must  produce  some  disturbing  effect  on  the  level 
of  the  ocean.  Suppose  the  earth  with  a  perfectly  smooth  surface, 
as  represented  by  a  model  globe,  then  the  center  of  gravity  corre- 
sponds with  the  center  of  the  figure,  and  the  ocean  must  form  a  film 
on  its  surface  of  the  same  depth  throughout.  Next  suppose  that 
islands  and  continents  are  modeled  in  clay  on  the  surface  of  the 
globe,  the  position  of  the  center  of  gravity  of  the  whole  mass  might, 
and  probably  would,  be  affected ;  but  the  disturbing  effect  on  the 
ocean  itself  will  be  more  readily  perceived  by  taking  separate 
account  of  the  additional  matter.  In  the  neighborhood  of  any  one 
of  these  patches  the  water  is  attracted,  as  before,  toward  the  center 
of  the  earth,  but  it  is  also  attracted,  more  or  less  horizontally,  to- 
ward the  additional  material.  Round  this,  then,  it  will  be  some- 
what heaped  up.  The  disturbance  will  be  slight  round  an  island, 
greater  round  a  continent,  still  greater  if  an  important  mountain 
chain  rises  near  the  coast.  Thus  changes  in  the  height  and  the  dis- 
tribution of  the  land  masses  must  react  upon  the  sea,  the  level  of 
which  may  be  affected  indirectly  by  distant  movements,  rather  than 
directly  by  the  rise  and  fall  of  the  actual  coast  line. 

These  undoubtedly  are  true  causes :  they  cannot  fail  to  produce 
an  effect ;  but  whether  they  are  adequate  to  produce  the  particular 
effects  which  have  to  be  explained  is  another  question.  The 
amount  of  the  disturbance  which  would  result  from  a  polar  ice  cap 
has  been  calculated.*  Supposing  the  latter  to  be  6000  feet  thick 
at  the  pole,  and  to  come  down  to  about  lat.  60°,  the  greatest 
height  to  which  it  would  raise  the  water  would  be  380  feet.  This 
amount  would  be  clearly  inadequate,  for  a  much  greater  elevation 
than  this  has  often  to  be  explained  ;  but  there  is  another  difficulty 
yet  more  serious :  the  old  water  marks  above  the  present  sea  level 
should  indicate  a  uniform  rise,  the  elevation  increasing  as  they  are 
followed  northward  along  a  parallel  of  longitude.  This  often  is  not 
the  case.  In  Norway,  on  the  actual  seacoast,  raised  beaches  and 
other  indications  of  the  change  of  level  are  seldom,  if  ever,  seen  in 

*  By  Sir  W.  Thomson  (Lord  Kelvin). 


MOVEMENTS  OF    THE   CRUST.  209 

the  southern  part  of  the  peninsula,  but  as  Trondhjem  is  approached 
they  begin  to  show  themselves,  and  become  conspicuous  to  the 
north  of  that  town.  Yet  if  any  one  of  the  fjords  be  entered,  raised 
beaches  soon  present  themselves,  and  generally  continue  to  increase 


FIG.  86.  DIAGRAM  OF  A  FAULT. 

x  y,  Line  of  fault;  a  i,  A  displaced  bed. 
The  beds  are  bent  near  the  fault  by  the  strain  in  slipping. 

in  elevation  toward  its  head.  Moreover,  in  one  and  the  same  dis- 
trict they  sometimes  vary  considerably  in  level,  and  are  not  uniform. 
According  to  observations  made  in  the  Alten  Fjord  the  variations 
in  the  level  of  the  same  terrace  amount  to  more  than  a  hundred  feet. 


FIG.  87. — DIAGRAM  OF  A  REVERSED  FAULT. 

Here  the  bed  b  has  been  pushed  up  over  a. 

Similar  objections  might  be  made  to  the  other  theories.  If  the 
total  quantity  of  the  water  were  diminished,  the  change  should  be 
everywhere  the  same ;  if  the  ocean  were  heaped  up  around  the 
larger  land  masses,  each  one  of  these  should  show  a  uniform  rise  ; 
both  theories  alike  would  be  inadequate  to  explain  the  effect  which 
has  been  observed.  We  may  therefore  conclude,  without  entering 


210  THE   STORY  OF  OUR  PLANET. 

upon  other  considerations,  that,  although  the  sea  level  cannot  be 
regarded  as  an  absolutely  fixed  datum  line,  the  surface  of  the  land 
does  actually  rise  and  fall. 

No  long  study  of  the  stratified  rocks  which  form  part  of  the 
earth's  crust  is  needed  to  show  that  these  movements  are  not  a  new 
thing  in  its  history.  The  gray  limestones,  in  which  the  dales  of 
Derbyshire  and  Yorkshire  are  excavated,  are  crowded  with  the 
remains  of  creatures  which  must  have  lived  and  died  not  only  in  the 


FIG.  88. — FLEXURES  IN  BEDDED  LIMESTONE,  DRAUGHTON,  NEAR  SKIPTON, 


ocean,  but  also  in  one  where  the  waters  were  clear.  The  slaty  rocks 
on  the  topmost  peak  of  Snowdon  are  full  of  fossil  shells  which  must 
once  have  inhabited  the  sea.  On  Alpine  summits,  at  elevations  of 
more  than  ten  thousand  feet,  marine  shells  are  found  embedded  in 
the  rocks,  while  in  the  Himalayas,  at  some  seventeen  thousand  feet, 
geologists  have  discovered  the  tests  of  a  large  foraminifer  very  nearly 
allied  to  one  which  may  be  picked  out  of  the  clays  sometimes  laid 
bare  by  the  sea  on  the  shore  of  Bracklesham  Bay  on  the  Sussex 
coast. 

These  facts  cannot  be  explained  by  any  theories  as  to  the  diminu- 
tion of  the  total  quantity  of  water  on  the  surface  of  the  globe,  for 
not  seldom  identically  the  same  fossils  can  be  discovered  in  one 


MOVEMENTS   OF    THE    CRUST.  21 1 

place  quite  close  to  the  present  sea  level,  in  another  many  hundreds 
of  feet  above  it.  Frequently  both  the  fossils  themselves  and  the 
characteristics  of  the  rock  indicate  that  it  has  been  formed  not  even 
on  a  coast,  but  in  the  clear  waters  of  the  open  ocean.  On  tracing 
the  rock  masses  over  a  considerable  area,  these  also  testify  to 
changes  of  level  subsequent  to  the  era  when  they  were  deposited, 
horizontally,  or  nearly  horizontally,  as  it  may  be  presumed,  on  the 
bed  of  the  sea.  The  strata  often  are  inclined  at  considerable  angles 
to  the  horizon  ;  sometimes  they  are  even  in  an  upright  position  ; 
they  are  bent  into  curves,  arches,  folds  of  all  kinds  (Fig.  88)  ;  they 
bear  the  marks  of  great  compression,  which  evidently  has  often 


FIG.  89.— DIAGRAM  OF  FOLDS  IN  STRATIFIED  ROCKS.    (COMPARE  FIG.  88.) 

acted  in  directions  quite  independent  of  the  planes  of  stratification  ; 
they  have  been  snapped  across  under  great  strains,  and  the  broken 
ends  are  now  separated  by  hundreds,  sometimes  even  thousands,  of 
feet — in  technical  language,  most  of  the  older  rocks,  and  some  of 
those  which  are  comparatively  modern,  have  obviously  suffered 
from  folding  and  faulting,  both  of  which  are  indicative  of  a  change 
of  level.  Every  mountain  range  testifies  to  these  movements,  often 
recurrent,  of  the  earth's  crust.  Two  instances — the  Jura  and  the 
Alps — may  suffice  as  an  illustration,  the  one  of  the  simpler,  the 
other  of  the  more  complex  structure.  As  we  hurry,  all  too  quickly, 
along  the  railway,  through  the  winding  glens  of  the  Jura,  we  cannot 
fail  to  notice  that  the  beds  of  cream-colored  limestone,  which  are 
exposed  in  cliff  and  scar,  often  slope  at  high  angles,  sometimes  in 
opposite  directions,  and  are  occasionally  curiously  contorted.  A 
more  careful  study  would  show  that  in  this  mountain  mass  alter- 
nating limestones  and  shales,  of  considerable  thickness,  have  been 
bent  into  a  group  of  parallel  folds,  from  which  the  present  scenery, 
the  rolling  ridges,  and  the  winding  dales,  have  been  sculptured  by 
the  action  of  those  natural  agencies  which  have  been  described  in 
earlier  chapters  of  this  book. 


212  THE   STORY  OF  OUR  PLANET. 

The  structure  of  the  Alps  is  more  complicated,  but  its  testimony, 
if  possible,  is  yet  stronger  than  that  of  the  Jura.  Different  parts  of 
this  great  mountain  chain  exhibit  differences  in  detail,  often  not 
unimportant,  but  in  all  cases  the  conclusion  to  which  their  testi- 
mony leads  is  the  same.  A  traverse  of  the  chain,  in  the  general 
direction  of  the  St.  Gothard  railway,  exhibits  its  structure  as  well  as 
any  other,  perhaps  better  than  most ;  it  has  also  the  advantage  of 
being  more  or  less  familiar  to  many  persons.  We  emerge  from  the 


FIG.  90.— DIAGRAM  OF  FAULTS  IN  STRATFIED  ROCKS. 

The  beds  a,  6,  c,  d,  if  unbroken,  would  follow  the  dotted  lines,  but  by  being  broken  and  dropped  down,  as 
shown  by  the  nearly  vertical  lines  at  c,  D,  E,  they  are  repeated  again  and  again.  A  u  represents  the 
present  surface  of  the  ground. 

Jura  upon  a  comparative  lowland — an  undulating  district,  where  the 
rounded  hills  and  gentle  slopes  seldom  rise  more  than  a  very  few 
hundred  feet  at  most  above  the  beds  of  the  rivers.  It  is  a  fair  and 
fertile  land — one  of  meadows  and  copses,  of  cornfields,  orchards,  and 
vineyards.  When  the  last  named  are  out  of  sight,  as  is  often  the 
case,  we  might  imagine  ourselves  in  some  rural  district  of  England, 
were  it  not  for  the  quaint  houses  dotted  about  here  and  there  on 
the  slopes  or  grouped  on  the  brink  of  a  stream,  or  for  glimpses  of  a 
mighty  mountain  wall,  away  to  the  south,  with  icy  peaks  that  gleam 
against  the  blue  sky.  But  presently  that  mountain  wall  rises  higher 
in  the  air,  and  is  more  and  more  sharply  defined.  The  details  of 
precipice  and  peak,  of  snowfield  and  glacier,  become  more  distinct ; 
the  hills  on  either  side  of  the  railway  begin  to  raise  more  boldly  ; 
their  slopes  are  steeper,  and  sometimes  even  broken  by  cliffs.  We 
have  now  reached  the  gate  of  the  mountains.  The  Lake  of  the 
Four  Forest  Cantons  spreads  its  clear  waters  between  the  meadow  of 


MOVEMENTS   OF    THE    CRUST. 


213 


Grutli  and  the  crags  of  the  Rigi.  These  crags  consist  mainly  of 
pudding  stone,  a  coarse  gravel  which  has  become  cemented  into  a 
mass  as  hard  as  concrete.  This  gravel  and  those  sandstones  which 
rise  by  the  lake  shore,  and  have  been  seen  at  intervals  on  the  low- 
land, are  composed  of  the  debris  of  an  ancient  mountain  chain,  and 
that  chain,  as  can  be  inferred  from  the  distribution  and  contents  of 
the  pebble  beds,  is  still  represented  by  the  Alps.  These  sands  and 
gravels  were  deposited  not  far  from  the  sea  level,  for  some  of  the 
former  even  contain  marine  shells,  while  the  latter  are  the  debris 
which  was  spread  abroad  by  rapid  rivers  as  they  emerged  from  the 


FIG.  91.— FOLDED  STRATA  (LOWER  TERTIARY)  IN  THE  HAUSSTOCK  (0.  Frass). 


gates  of  the  hills.  But  now  these  gravels  sometimes  rise  full  five 
thousand  feet  above  sea  level,  so  that  since  they  were  deposited  the 
land  must  have  been  greatly  uplifted.  This,  however,  is  not  all. 
The  mountains  which  they  form  are  but  the  outworks  of  the  Alps  ; 
behind  them  rises  a  line  of  loftier  and  bolder  summits,  ranging  often 
from  about  six  thousand  to  ten  thousand  feet  above  sea  level,  occa- 
sionally reaching  a  still  greater  elevation.  In  these  limestone  is  the 
dominant  rock,  but  slaty  or  shaly  beds  are  common — pebble  beds 
and  sandstones  are  rare.  At  first  sight  their  relation  to  the  last- 
named  group  is  rather  perplexing — in  most  places  they  appear  to 
rise  from  beneath  them,  but  in  others  to  overlie  them.  Further 
examination,  while  it  justifies  the  perplexity,  explains  the  apparent 
contradiction.  These  beds  are  often  curiously  bent  and  folded,  as 
may  be  seen  in  the  fine  cliffs  which  are  mirrored  in  the  Bay  of  Uri. 
But  in  some  places  this  process  has  been  carried  so  far  that  the  folds 


214 


THE   STORY  OF  OUR  PLANET. 


have  been  pushed  over  from  the  southern  side  till  their  loops  have 
been  doubled  back.  As  the  thrust  continued,  these  sometimes 
yielded  to  the  strain,  and  the  upper  half  was  then  pushed  for  some 
distance  above  the  lower,  thus  bringing  the  inner  or  older  member  of 
the  fold  to  rest  upon  the  outer  or  newer  (Fig.  92).  In  the  language 
of  geology  this  is  termed  an  over- 
thrust  fault ;  it  brings  the  beds  into  a 
wrong  order,  and  is  often  (in  the  ab- 
sence of  fossils)  extremely  difficult  to 
detect.  As  the  road  passes  away  from 
the  head  of  the  lake,  up  the  valley  of 
the  Reuss,  the  whole  thickness  of  the 
mountain  mass  for  a  time  is  composed 
of  these  limestone  rocks ;  but  at  Erst- 
feld  their  foundation  stones  are  dis- 
closed, as  a  new  group  of  rocks  appears 
beneath  them  and  rises  rapidly  upward. 
After  passing  Amsteg  little  more  is 
seen  of  the  sedimentary  deposits,  for 
the  left  bank  of  the  Maderanerthal  con- 
sists almost  entirely  of  crystalline  rocks 
(Fig.  93).f  For  several  miles  the  wild 
glens  of  the  Reuss  and  the  snow- 
streaked  peaks  above  are  wholly  sculp- 
FIG.  92.— PROCESS  OF  CONVERSION  tured  from  this  group— a  hard,  gray, 
3UGHAN  granite-like  rock  being  the  com- 
Through  this  are  driven  the 
curious  corkscrew  tunnels  of  the  rail- 
way ;  into  this  it  disappears  at  Goschenen,  as  it  begins  its  subter- 
ranean journey,  more  than  three  leagues  long,  through  the  water- 
shed of  Europe.  The  same  rock  continues  to  the  Devil's  Bridge, 
but  after  the  road  has  emerged  from  the  "  Hole  of  Uri  "  the  scene 
suddenly  changes.  Instead  of  the  narrow  glens  and  frowning  crags 
a  comparatively  broad  and  fertile  valley  opens  out  in  front,  guarded 
on  one  side  by  the  chain  which  has  been  traversed,  on  the  other  by 
one  in  many  respects  similar,  but  rather  less  bold  in  outline.  The 
latter  is  the  watershed  of  Europe.  Parallel  with  this  the  valley  of 
the  Reuss  extends  for  a  few  miles,  but  from  any  commanding  peak 
it  would  be  seen  to  be  carved  out  of  the  floor  of  a  great  trough 


OVERFOLD  \K\  INTO   AN   OVER- 

THRUST  FAULT  [<•].  monest. 


These  are  schists,  gneissose  and  granitoid  rocks. 


MOVEMENTS  OF   THE   CRUST. 


215 


which  is  occupied  by  the  head  waters,  not  only  of  the 
also  of  the  Rhine  on  one  side  and   of  the   Rhone  on 

So  marked  a  change  of  scenery  is  a  sure 
indication  of  a  change  in  the  rocks.  The 
geological  structure  just  in  this  part  is  ex- 
tremely complicated,  and  some  of  its  details 
are  still  the  subject  of  controversy ;  but  this 
trough,  speaking  in  general  terms,  is  formed 
by  a  mass  of  slaty  rock,  the  greater  part  of 
which  is  very  nearly  of  the  same  age  as  the 
limestones  which  were  last  seen  in  the 
neighborhood  of  Amsteg.  It  is  part  of  a 
huge  fold,  caught  between  the  masses  of 
underlying  crystalline  rock.  From  the 
meadows  of  Andermatt  and  Hospenthal  the 
road  mounts  toward  the  St.  Gothard  Pass, 
again  traversing  schists,  gneisses,  and  gran- 
ites, though  different  in  some  respects  from 
those  previously  seen  ;  but  at  Airolo,  where 
it  arrives  at  the  foot  of  the  steeper  descent, 
and  at  the  southern  mouth  of  the  tunnel,  it 
finds  a  similar  trough-like  valley  and  deposits 
of  a  like  age  to  those  on  the  other  side  of 
the  range,  though  the  fold  is  on  a  smaller 
scale.  But  even  here  these  gigantic  wrink- 
lings of  the  earth's  crust  are  not  ended. 
As  is  shown  in  the  excellent  section  given 
in  Prof essor . Prestwich's  "Geology,"*  four 
sharply  infolded  troughs  have  yet  to  be 
crossed,  with  the  intervening  uplifts,  before 
the  road  comes  to  the  border  zone  of  sand- 
stone shortly  beyond  which  the  plain  of 
Northern  Italy  is  reached,  and  the  Alps  are 
finally  left  behind.  To  what  kind  of  move- 
ment in  the  earth's  crust  is  a  structure 
such  as  that  which  the  Alps  exhibit  to  be 
ascribed  ?  By  placing  a  number  of  thin  slabs 
of  some  imperfectly  flexible  materials  one 
upon  the  top  of  another,  and  by  then  bringing 


Reuss,  but 
the    other. 


*Vol.  i.  ("Chemical  and  Physical")  p.  304. 


2l6 


THE   STORY  OF  OUR  PLANET. 


the  opposite  ends  gradually  closer  together,  the  folds,  and  even 
some  of  the  peculiar  fractures  and  faulting,  of  a  mountain  chain  can 
be  imitated  (Fig.  94).*  It  seems,  then,  most  natural  to  attribute  a 
mountain  chain  to  the  effects  of  lateral  pressure,  this  being  due  to  a 
contraction  of  the  earth's  crust  through  the  loss  of  internal  heat. 

Such  an  explanation,  however,  is  not  without  its  difficulties,  as 
will  be  seen  later  on,  and  a  different  solution  of  the  problem  was 
offered  a  few  years  since  by  Mr.  Mellard  Reade.  This  makes  the 
"ridging  up"  of  the  crust  an  indirect,  rather  than  a  direct,  conse- 
quence of  radiation  of  heat.  Most  substances  expand  when  their 


FIG.  94.— DIAGRAM  ILLUSTRATING  PROFESSOR  FAVRE'S  EXPERIMENT. 

Showing  the  artificial  folds  produced   in  a  series  of  layers  of  clay  on  indiarubber,  according  to  an  experi- 
ment of  Professor  A.  Favre.     The  arrows  show  the  direction  of  the  contraction. 


temperature  is  raised.  If,  however,  as  he  shows  by  experiments, 
any  material,  such  as  a  plate  of  metal,  be  fastened  down  securely  at 
the  edges,  so  that  expansion  in  any  but  a  vertical  direction  becomes 
impossible,  and  its  temperature  be  raised,  then  it  is  bent  into 
puckers  and  waves  something  like  those  of  a  mountain  chain.  A 
mass  of  rock,  forming  part  of  the  crust  of  the  earth,  is  under  some- 
what similar  conditions.  When  its  temperature  is  raised,  expansion 
downward  is  resisted  by  the  mass  beneath,  and  laterally  by  the  rest 
of  the  crust,  while  in  an  upward  direction  gravity  alone  has  to  be 
overcome.  If,  then,  any  part  of  the  crust  be  raised  to  a  higher 
temperature,  the  result  must  be  puckering  and  folding,  especially  in 
the  more  superficial  part. 

So  Mr.  Reade  supposes  that  a  mountain  range  has  been  produced 
in  the  following  way:  In  the  first  place,  some  unequal  movements 


*  This  has  been  done  in  models  prepared  by  Professor  Favre,  which  are  preserved  in  the 
Geological  Museum  at  Geneva,  and  in  a  remarkable  series  made  by  Mr.  H.  M.  Cadell, 
and  described  by  him  in  a  paper  published  in  the  "  Transactions  of  the  Royal  Society  of 
Edinburgh,"  vol.  xxxv.  p.  337. 


MOVEMENTS  OF    THE    CRUST.  217 

caused  upheaval  in  one  considerable  area  of  the  crust  and  depression 
in  another  adjoining ;  the  former  must  become  a  region  of  denuda- 
tion, the  latter  one  of  deposition.  Suppose  this  process  to  be  con- 
tinued for  a  long  time,  and  a  great  thickness  of  sediment  to  have 
been,  as  it  were,  plastered  over  a  zone  of  the  crust  (for  it  must  be 
remembered  that,  as  already  pointed  out,  most  of  the  sediment 
brought  down  into  the  sea  is  deposited,  as  a  rule,  within  a  limited 
distance  from  the  land).  Then  if  the  interior  of  the  earth,  as  is 
generally  believed,  be  at  a  high  temperature,  and  heat  is  being  lost 
by  radiation,  the  effect  of  this  local  addition  to  the  thickness  of  the 
crust  will  be  like  that  of  cementing  a  strip  of  non-conducting 
material  on  the  surface  of  a  cooling  ball  of  metal :  the  temperature 
of  the  mass  immediately  beneath,  and  ultimately  that  of  the  strip 
itself,  will  be  raised.  Thus  both  the  sedimentary  deposits  and  the 
floor  on  which  they  rest  expand,  and,  as  movement  is  only  pos- 
sible in  an  upward  direction,  puckering  and  folding  are  produced.* 
But  the  underlying  rock  consists  of  much  less  pliant  materials  than 
the  overlying ;  for,  as  greatly  the  older,  they  are  more  consolidated, 
perhaps  are  even  crystalline,  and  this  inequality  must  introduce 
complications  in  the  process  of  folding.  Moreover,  as  the  tempera- 
ture of  the  floor  gradually  rises,  this  may  be  sufficient  locally  to 
soften  portions  of  it  which  previously  had  been  solid ;  hence  the 
foundation  itself  might  be  fractured  under  strain,  and  thus  new 
complications  might  be  introduced.  Again,  as  the  freshly  disturbed 
mass  began  to  rise  it  too  would  be  exposed  to  denudation.  But 
as  the  exterior  was  carved  into  hill  and  valley,  the  temperature  of 
the  crust  beneath  would  be  affected.  The  surfaces  of  equal  tem- 
perature in  it  would  reproduce,  to  a  certain  extent,  the  irregularities 
of  the  outer  surface,  and  the  contractions  thus  caused  would  intro- 
duce further  complications  into  the  foldings.  The  result  of  all  these 
irregularities  might  be  the  inversions,  overthrusts,  and  other  more 
local  and  exceptional  disturbances  which  occur  in  a  mountain  region. 
Mr.  Mellard  Reade's  reasoning  is  sound  and  coherent;  a  period  of 
mountain  making  appears  generally  to  have  been  preceded  by  one 
of  depression  and  deposition ;  foldings  and  other  disturbances 
undoubtedly  might  be,  and  probably  often  have  been,  produced  as 
he  describes  ;  his  hypothesis  avoids  the  main  difficulty  (which  is  not 
inconsiderable)  in  the  other  explanation.  At  the  same  time  doubts 
may  be  felt  whether  it  is  not  attended,  when  applied  as  a  working 

*  The  effect,  of  course,  is  much  greater  in  the  lower  part  of  the  zone  of  added  material  ; 
radiation  produces  practically  no  alteration  in  the  surface  temperature  of  the  earth. 


218  THE   STORY  OF  OUR  PLANET. 

hypothesis,  with  difficulties  which  are  quite  as  serious.  The  folding 
of  a  chain  like  the  Alps  is  so  marked,  and  its  scale  so  gigantic,  that 
the  difference  of  temperature  and  consequent  expansion  which 
would  be  produced  by  the  accumulation  on  that  area  of  a  few 
thousand  feet  of  rock  seem  quite  inadequate  as  a  cause,  while  the 
evidence  that  the  thrusts  have  been  mainly  lateral  seems  very  strong. 
Not  only  the  softer  sedimentaries,  but  even  the  hard  crystalline 
masses  are  commonly  affected  by  a  cleavage  structure,  which  makes 
a  high  angle  with  the  horizon,  and  must  accordingly  be  the  result  of 
a  pressure  which  has  acted  nearly  parallel  with  the  latter.  Though 
the  amount  of  surface  which  must  be  lost  by  the  formation  of  a 
mountain  chain  by  contraction  of  the  crust  seems  large  when 
expressed  in  miles,  this  can  be  obtained  by  a  shortening  of  the 
radius,  relatively  very  small,  the  effect  of  which  on  the  rate  of  rota- 
tion of  the  globe  may  be  counterbalanced  by  other  agencies,  and  by 
the  "  drag  "  of  the  tidal  waves.  Thus  it  is  probably  more  correct  to 
attribute  the  origin  of  mountain  ranges  to  a  contraction  in  the  crust 
which  is  the  result  of  loss  of  heat  in  the  globe  as  a  whole,  rather 
than  to  the  combined  effect  of  radiation  and  deposition,  which  Mr. 
Reade  regards  as  the  dominant  cause. 

Two  eminent  Austrian  geologists  *  have  called  attention  to 
another  way  in  which  the  loss  of  heat  in  producing  contraction  may 
affect  the  level  of  the  crust.  As  this  crust  is  not  homogeneous  in 
composition  or  uniform  in  strength,  some  portions  of  it  may  sub- 
side, while  others  remain  at  rest.  The  following  illustration  which 
they  offer  gives  in  a  few  words  a  general  idea  of  their  hypothesis : 
Suppose  that,  for  simplicity,  any  portion  of  the  upper  part  of  the 
earth's  crust  be  represented  by  a  sheet  of  ice  covering  the  surface 
of  a  lake,  and  that  from  its  bed  either  piles  or  pieces  of  masonry  rise 
up  here  and  there  so  as  to  just  touch  the  bottom  of  the  ice.  If  some 
of  the  water  be  drawn  off,  the  ice  above  these  obstacles  f  remains 
immovable,  but  that  in  the  interval  sinks,  cracking  and  bending  as 
it  slips  down  along  their  flanks,  in  the  immediate  vicinity  of  which 
the  most  marked  disturbances  will  be  produced.  The  piers  repre- 
sent ancient  masses  of  solid  crystalline  rocks ;  the  ice  the  less 
coherent  sediments  deposited  on  and  about  them.  In  this  view  the 
changes  of  level  are  due  to  subsidence  rather  than  to  upheaval,  for 


*  Professor  Suess  ("  Antlitz  der  Erde  ")and  Neumayer  ("  Erdegeschichte  "). 
f  Such  a  mass  is  called  Hurst,  from  a  miner's  term  which  means  a  pillar,  mound,  or  point 
of  rock. 


MOVEMENTS  OF   THE   CRUST.  219 

the  original  level  of  the  seas  is  represented  by  the  fragments  of  sedi- 
mentary deposits  which  still  cover  the  piers,  and  those  which  remain 
often  comparatively  unaffected  by  denudation,  in  the  intervening 
spaces,  have  descended,  like  the  present  ocean,  toward  the  center 
of  the  earth. 

This  hypothesis  gives  a  very  natural  explanation  of  the  present 
disposition  of  the  Secondary  Rocks  in  some  parts  of  Europe  ;  for 
instance,  in  France  they  are  disposed  about  the  central  plateau  of 
Auvergne,  with  the  Cevennes,  the  massif  Q{  Brittany  and  that  of 
the  Vosges,  in  a  series  of  basins,  with  the  edges  of  the  older 
deposits  nearer  to  the  districts  which  consist  of  ancient  crystalline 
rocks,  each  succeeding  the  other,  like  the  edges  of  a  series  of  thick 
saucers  which  gradually  diminish  in  size  and  are  placed  one  within 
the  other.  It  is  also  applicable  to  other  parts  of  Europe,  but  it< 
seems  hardly  adequate  to  account  for  such  a  broad  zone  of  sharp 
folds  as  is  presented  by  the  Alps  and  several  other  mountain  chains. 
May  not  contraction  produce  sometimes  the  one  result,  sometimes 
the  other,  according  to  circumstances,  this  being  the  effect,  so  to 
say,  of  the  surface  dimpling,  that  of  its  wrinkling?  In  either  case 
the  resistance  to  movement  which  is  offered  by  large  masses  of 
rock  more  solid  than  other  parts  similarly  affected  cannot  fail  to 
modify  profoundly  the  results  produced  either  by  vertical  shrinkage 
or  by  tangential  thrust.  This  is  one  of  the  many  geological  ques- 
tions on  which,  as  our  knowledge  is  so  rapidly  growing,  it  is  wiser 
to  "  keep  an  open  mind,"  for  what  would  be  a  weakness  in  politics 
may  be  a  duty  in  science. 


CHAPTER  II. 

VOLCANIC   ACTION  AND   ITS   EFFECTS. 

VOLCANOES  are  external  indications  of  inward  disturbances — 
symptoms,  like  boils  upon  the  body,  of  constitutional  derangement 
in  the  globe,  and  in  this  case,  as  in  the  other,  doctors  are  not  always 
agreed  in  their  diagnosis  of  the  malady.  A  volcano  is  an  orifice  in 
the  crust  of  the  earth,  commonly  terminating  in  a  bowl-like  hollow, 
'called  a  crater,  which  forms  the  summit  of  a  mountain  or  hill, 
usually  more  or  less  conical  in  outline.  From  the  crater  are 
ejected — sometimes  continuously,  sometimes  with  long  intervals  of 
quiescence,  but  always  more  or  less  explosively — gas,  steam  or 
water,  dust  (formed  of  comminuted  minerals  or  rock),  scoria  or  bits 
of  natural  slag,  and  molten  rock  or  lava.  Sometimes  there  is  a 
well-marked  central  cone,  which  crowns  a  lofty  mountain  mass. 
The  outlines  of  this  may  bear  general  resemblance  to  those  of  the 
upper  portion,  though  usually  it  has  been  furrowed  by  streams  and 
wasted  by  rains — in  a  word,  considerably  modified  by  processes  of 
denudation.  The  highest  point  in  the  crater  may  rise  to  an  elevation 
of  several  thousand  feet,  not  only  above  the  sea,  but  even  above 
the  surrounding  plateaus,  as  Cotopaxi  rises  more  than  nine  thousand 
feet  above  the  plain  at  its  base,*  or  the  Peak  of  Teneriffe  towers 
above  the  ocean  to  an  altitude  of  over  twelve  thousand  feet. 
Sometimes  the  craters,  as  in  the  Phlegraean  Fields,  are  low  in  pro- 
portion to  their  height,  and  form  irregular  inconspicuous  groups 
without  any  dominant  summit.  Sometimes  the  cones  take  a  linear 
order,  more  or  less  simple,  and  help  to  make  up  a  vast  mountain 
chain,  as  in  the  Andes ;  sometimes  they  rise  in  solitary  grandeur, 
like  Etna.  But  as  volcanoes  are  studied  the  one  type  seems  to 
merge  into  the  other,  and  a  classification  by  forms  or  by  distribu- 
tion appears  almost  impossible.  Neither  does  it  seem  more  feasible 
to  classify  volcanoes  by  the  character  of  their  emissions.  From 
the  same  orifice  different  materials  may  be  discharged  at  different 
times:  at  an  epoch  of  quiescence,  gas  or  steam;  at  one  of  greater 

*  Whymper,  "  Travels  in  the  Great  Andes  of  Ecuador,"  vol.  i.  ch.  vi. 


VOLCANIC  ACTION  AND   ITS  EFFECTS. 


activity,  hot  water,  mud,  or  clouds  of  dust ;  at  its  greatest  intensity, 
showers  of  scoria  and  streams  of  lava.  Specialized  varieties,  as  they 
may  be  called,  may,  no  doubt,  be  found :  volcanoes  where  local 
circumstances  restrict  the  eruptive  discharge  within  a  more  limited 
range,  like  the  craters  of  boiling  mud  at  Kravla,  in  Iceland,  or  the 
geyser  fountains  of  boiling  water  in  that  country  or  at  the  Yellow- 
stone ;  but  all  these  are  so  closely  connected  as  to  be 
only  varietal  manifestations  of  the  same  set  of  causes. 
In  a  volcanic  eruption  the  earth  trembles,  and  the  air 
is  dark  with  the  ejected  dust,  which  spreads  over  miles 
of  country  a  murky  pall  even  more  hideous  than  a 
midday  fog  in  London.  The  crater  is  veiled  in  clouds 
of  steam,  fetid  with  acid  vapors  ;  these  at  one  time 
white  as  a  mass  of  cumulus,  at  another  are  blackened 
with  the  dust,  and  at  night  are  glowing  with  the 
reflected  glare  of  the  molten  mass  within  the  crater ; 
on  the  flanks  of  the  mountain  blocks  of  rock  fall  hurt- 
ling through  the  air,  and  at  last  the  molten  lava  from 
the  vast  subterranean  furnace  creeps  down  the  slopes 
beneath  a  pall  of  steam,  its  path  marked  by  destruc- 
tion, and  irresistible  as  death.  The  scene  is  a  realiz- 
ation of  a  prophet's  vision  of  the  time  when 


Dies  iras,  dies  ilia,  Solvet  sasculum  in  favilla. 


FIG.  95.— 

AN  EJECTED 

CLOT    OF 

LAVA. 


But  there  is  nothing  without  a  reason,  and  the  question  arises, 
What  cause  or  combination  of  causes  produces  these  rude  interrup- 
tions, happily  local,  to  the  general  tranquillity  of  the  order  of 
Nature?  An  answer  to  this  must  be  sought  in  studying  not  only 
the  phenomena  of  a  volcanic  eruption,  but  also  the  structure  of 
volcanoes  themselves.  Just  as  the  physician  obtains  his  knowledge 
not  only  by  watching  the  progress  of  a  disease  in  his  clinical  studies, 
but  also  by  investigation  of  the  morbid  tissues  in  the, dissecting 
room,  so  the  geologist  must  draw  his  inferences  from  volcanoes; 
for  they,  like  all  other  things,  have  their  time  to  die,  and  then  the 
corpse,  though  too  gigantic  for  the  puny  tools  of  man,  is  dissected 
by  his  ministrants,  and  made  into  preparations  for  his  study.  In 
other  words,  volcanoes  may  be  found  which  exhibit  every  stage, 
from  the  perfect  crater — of  which,  as  it  seems,  the  last  discharge  of 
steam  or  gas  was  an  event  almost  of  yesterday — to  the  ruined  mass 
where  crater  and  cone  alike  have  disappeared,  and  the  bare  skeleton 
can  be  recognized  only  by  the  practiced  eye. 


222 


THE   STORY  OF  OUR  PLANET. 


The  clinical  study  shall  have  first  place  in  this  notice,  but  it  will 
be  well  to  call  attention  at  the  outset  to  a  fact  which  will  prove  to 
have  a  pathological  significance.  Water  and  volcanic  eruptions 
seem  closely  connected.  Volcanoes  on  the  land  are,  indeed,  more 
conspicuous  than  those  under  the  sea  ;  but  submarine  volcanoes  are 
not  rare,  and  even  the  former  are  almost  invariably  near  to  the 
ocean  or  to  some  large  sheet  of  water. 

The  number  of  volcanic  eruptions  which  have  been  recorded  with 
more  or  less  care  and  precision  is  now  so  large  that  it  is  by  no 


FIG.  96. — MUD  VOLCANOES,  TURBACO,  COLOMBIA. 

means  easy  to  make  a  selection  of  cases  which  may  serve  as  types. 
That  which  we  place  first  in  order  is  chosen  as  one  of  the  simplest 
examples,  yet,  at  the  same  time,  one  of  the  most  complete,  for  it 
exhibits  the  building  of  a  volcanic  cone  from  beginning  to  end,  all  in 
the  course  of  a  very  few  days.  It  is  that  of  Monte  Nuovo  on  the 
Bay  of  Baiae.  This  cone  rises  on  ground  classic  to  the  student  of 
literature  as  well  as  of  science.  Here  Horace  and  the  men  of  the 
Augustan  age  loved  to  linger  ;*  yet  here,  too,  was  the  dark  entrance 
to  the  world  of  shadows.f  Shore  and  land  are  studded  both  with  the 
ruins  of  Roman  luxury  and  with  the  craters  of  volcanoes,  so  con- 


*Nullus  in  orbe  sinus  Baiis  praelucet  amoenis." — Hor.,  "  Ep."  i,  i.  83. 
f  Lake  Avernus,  occupying  an  old  crater. 


VOLCANIC  ACTION  AND  ITS  EFFECTS. 


223 


•spicuous  that  ages  since  the  land  was  named  Campi  Phlegraei,  or  the 
Burning  Fields.  These  volanic  hills  on  the  west  of  Naples  are  a 
curious  contrast  to  Vesuvius  on  the  east.  There  a  mountain  mass, 
with  a  central  cone,  rises  to  a  height  of  nearly  five  thousand  feet 
above  the  sea.  Here  are  several  craters,  broad  in  comparison  with 
their  height,  for  they  do  not  attain  to  more  than  a  few  hundred  feet 
above  sea  level ;  yet  the  crater  ring  of  the  largest — Astroni — is  three 
miles  in  circumference,  and  its  inner  area  spacious  enough  to  serve 
as  a  royal  deer  park.  Some  of  these  craters  have  long  since  ceased 
to  be  active,  and  are  in  ruins ;  others  have  been  occasionally, 


FIG.  97. — MONTE  Nuovo,  FROM  THE  SEA-SHORE. 

though  rarely,  in  eruption,  but  in  them  an  isolated  jet  of  steam  or  a 
pond  of  boiling  mud  indicates  the  possibility  of  .future  disturbances. 
Rather  more  than  a  mile  to  the  west  of  the  ruins  of  the  Temple  of 
Serapis,  mentioned  in  the  last  chapter,  lies  the  Lucrine  Lake,  the 
basin  of  an  old  crater  which  in  the  days  of  Augustus  was  connected 
with  the  sea.  Such  a  natural  harbor  on  this  shallow  coast  would  be 
welcome  to  the  Roman  mariner ;  the  place  also  was  acceptable  to 
the  Roman  epicure  as  producing  the  best  oysters  in  Italy.' 

Thus  runs  the  story  of  the  building  of  Monte  Nuovo,  as  it  is  told 
by  some  contemporary  writers  :  For  two  years  prior  to  September, 
1538,  Naples,  Pozzuoli,  and  its  neighborhood  had  been  frequently 
shaken  by  earthquakes.  At  last,  on  the  2Qth  of  that  month,  about 
an  hour  after  midnight,  flames  of  fire  *  appeared  on  the  shore  on  the 
present  site  of  Monte  Nuovo  ;  the  ground  rose,  and  a  not  incon- 
siderable tract  of  the  shallow  sea  became  land.  Then  cracks  were 


*  Probably  steam  reflecting  the  glowing  material  beneath. 


224  THE   STORY  OF  OUR  PLANET. 

seen  to  open  near  to  the  Lucrine  Lake,  and  from  the  "  horrid 
mouth  "  thus  disclosed  "  were  vomited  furiously  smoke,  fire,  stones, 
and  mud  composed  of  ashes  ";  the  discharge  was  accompanied  by  a 
noise  like  the  loudest  thunder,  and  some  of  the  masses  ejected 
"  were  larger  than  an  ox.  .  .  The  stones  went  about  as  high  as  a 
crossbow  can  carry,  and  then  fell  down,  sometimes  on  the  edge,  and 
sometimes  into  the  mouth  itself.  The  mud  was  of  the  color  of 
ashes,  and  at  first  very  liquid,  then  by  degrees  less  so,  and  in  such 
quantities  that  in  less  than  twelve  hours,  with  the  help  of  the  above- 
mentioned  stones,  a  mountain  was  raised  of  one  thousand  paces  in 
height.  Not  only  Pozzuoli  and  the  neighboring  country  was  full  of 
this  mud,  but  the  city  of  Naples  also,  so  that  many  of  its  palaces 
were  defaced  by  it.*  Now  this  eruption  lasted  two  days  and  two 
nights  without  intermission,  though,  it  is  true,  not  always  with  the 
same  force.  The  third  day  the  eruption  ceased,  and  I  went  up  with 
many  people  to  the  top  of  the  new  hill  and  saw  down  into  its 
mouth,  which  was  a  round  cavity  about  a  quarter  of  a  mile  in  cir- 
cumference, in  the  middle  of  which  the  stones  which  had  fallen  were 
boiling  up,  just  as  a  caldron  of  water  boils  on  the  fire.  The  fourth 
day  it  began  to  throw  up  again,  and  the  seventh  much  more,  but 
still  with  less  violence  than  the  first  night.  .  .  In  the  day  the 
smoke  still  continues,  and  you  often  see  fire  in  the  midst  of  it  in 
the  night  time."f 

The  cone  of  Monte  Nuovo  rises  to  a  height  of  440  feet  above  the 
sea;  the  vent  is  completely  sealed,  neither  steam  nor  gas  being 
exhaled.  The  outer  slopes  are  clothed  with  coarse  herbage,  heath, 
and  broom,  or  with  oak  scrub,  mulberry,  ilex,  and  stone-pine ;  the 
inner  slopes  descend  very  steeply  to  a  saucer-shaped  basin,  culti- 
vated (in  1876)  as  a  garden.  A  study  of  the  cone  fully  confirms  the 
inference  suggested  by  the  testimony  quoted  above,  viz.,  that  it 
was  built  up  by  the  materials  discharged  from  the  orifice,  and  that 
any  elevation  of  the  land  was  a  factor  in  its  structure  comparatively 
unimportant.:}: 

We  pass  from  Italy  to  the  Sandwich  Islands.  About  4000  feet 
above  sea  level,  on  the  flank  of  Mauna  Loa — almost  the  highest 


*  Probably  this  was  dust  shot  up  in  a  state  of  fine  division  among  steam  to  a  very  con- 
siderable height,  and  brought  down  mingled  with  rain. 

f  Quoted  in  Sir  C.  Lyell's  "Principles  of  Geology,"  ch.  xxiv.,  from  Sir  W.  Hamilton's 
"  Campi  Phelgrnei,"  p.  70. 

\  Four  different  accounts  are  quoted  by  Sir  C.  Lyell  ("  Principles,"  ch.  xxiv.),  which, 
though  they  differ  as  to  minor  details,  agree  in  their  more  important  features. 


VOLCANIC  ACTION  AND   ITS  EFFECTS.  225 

mountain,  and  itself  a  volcanic  cone,  frequently  in  eruption — some 
twenty  miles  away,  is  the  singular  subsidiary  crater  of  Kilauea.  It 
is  a  huge  basin,  practically  without  a  cone  ;  in  other  words,  hardly 
more  than  an  orifice  in  the  gently  shelving  flank  of  the  massif 
of  Mauna  Loa,  in  form  an  irregular  oval  with  a  projecting  end; 


FIG.  98. — THE  ISLAND  OF  HAWAII  IN  THE  HAWAIIAN  OR  SANDWICH  GROUP, 
SHOWING  THE  DIFFERENT  CRATERS  AND  THE  LAVA  STREAMS  OF  VARIOUS  ERUPTIONS. 

(.a)  Hualalai ;  (£)  Mokuaweoweo;  (V)  Kilauea— craters  ;  (rf)  lava  streams.     The  contour  lines  show 
differences  of  2000  feet  in  height. 

it  is  about  2*4  miles  long,  and  its  precipitous  walls  inclose  an 
area  of  nearly  four  square  miles.  A  well-marked  and  generally 
broad  ledge  or  step  divides  the  crater  into  two  stages.  The  floor  in 
1887  was  "  a  desolate  scene  of  bare  rock.  Instead  of  a  sea  of  molten 
lava  '  rolling  to  and  fro  its  fiery  surge  and  flaming  billows/  *  the  only 
signs  of  action  were  in  three  spots  of  a  blood-red  color,  which  were 
in  feeble  and  constant  agitation,  like  that  of  a  caldron  in  ebullition. 
Fiery  jets  were  playing  over  the  surface  of  the  three  lakes,  but  it 
was  merely  quiet  boiling,  for  not  a  whisper  was  heard  from  the 
depths.  And,  in  harmony  with  the  stillness  of  the  scene,  white 
vapors  rose  in  fleecy  wreaths  from  the  pools  and  numerous  fissures, 
and  collected  over  the  large  lava  lake  into  a  broad  canopy  of 
clouds.  .  .  When  on  the  verge  of  the  lower  pit,  a  half-smothered 

*  As  it  had  been  described,  perhaps  somewhat  poetically,  by  a  previous  observer. 


226  THE    STORY   OF  OUR   PLANE 7'. 

gurgling  sound  was  all  that  could  be  heard.  Occasionally  a  report 
like  musketry  came  from  the  depths ;  then  all  was  still  again,  except 
the  stifled  mutterings  of  the  boiling  lakes.  In  a  night  scene  from 
the  summit  the  large  caldron,  in  place  of  a  bloody  glare,  now 
glowed  with  intense  brilliancy,  and  the  surface  sparkled  all  over 
with  shifting  points  of  dazzling  light,  like  '  a  network  of  lightning/ 
occasioned  by  the  jets  in  constant  play;  at  the  start  of  each  the 
white  light  of  the  depths  breaking  through  to  the  surface.  A  row 
of  small  basins  on  the  southeast  side  of  the  lake  were  also  jetting 
out  their  glowing  lavas.  The  two  smaller  lakes  tossed  up  their 
molten  rock  much  like  the  larger,  and  occasionally  there  were 
sudden  bursts  to  a  height  of  forty  or  fifty  feet.  The  broad  canopy 
of  clouds  above  the  pit,  and  the  amphitheater  of  rocks  around  the 
lower  depths,  were  brightly  illumined  from  the  boiling  lavas,  while 
a  lurid  red  tinged  the  more  distant  walls,  and  threw  into  varying 
depths  of  blackness  the  many  cavernous  recesses."  * 

From  the  top  of  the  outer  wall  of  the  crater  of  Kilauea  to  the 
surface  of  the  molten  rock  is  generally  rather  more  than  a  thousand 
feet,  the  inner  pit  being  some  400  or  500  feet  deep.  But,  as  Pro- 
fessor Dana  has  shown  in  his  exhaustive  study  of  the  volcano,  these 
measurements  and  many  of  the  details  are  liable  to  great  variation ; 
the  molten  rock  occasionally  floods  the  lower  ledge,  and  even  rises 
high  up  in  the  outer  crater.  But  paroxysmal  eruptions  are  rare, 
and  generally  on  a  small  scale.  Kilauea  is  a  huge  caldron  of 
molten  rock,  the  surface  of  which  becomes,  to  a  very  great  extent, 
covered  with  a  crust  during  times  of  comparative  exhaustion,  from 
which  also  no  large  quantity  of  steam  is  discharged.  Showers  of 
dust  and  scoria  are  few;  it  is  like  the  mouth  of  a  great  smelting 
furnace,  which  on  rare  occasions  threatens  to  overflow,  but  even 
then  in  consequence  of  a  quiet  swelling  up  of  its  molten  contents, 
rather  than  of  the  usual  series  of  violent  explosions. 

Krakatoa,  a  volcanic  island  in  the  Straits  of  Sunda,  supplied,  a 
few  years  ago,  an  instance  of  the  terrific  outbreak  of  the  volcanic 
forces  after  a  long  period  of  quiescence.  The  island  has  had  a  varied 
history,  but  of  its  earlier  chapters  no  record  has  been  preserved. 
Here,  at  some  unknown  period,  a  large  cone,  the  base  of  which  may 
have  measured  five-and-twenty  miles  in  circumference,  rose  to  a 
height,  perhaps,  of  at  least  10,000  feet.  At  a  later  period,  equally 
unknown,  an  eruption,  or  a  series  of  eruptions,  blew  away  this  cone, 

*  Professor  J.  D.  Dana,  '  Characteristics  of  Volcanoes,"  p.  68. 


VOLCANIC  ACTION  AND  ITS  EFFECTS. 


227 


leaving  behind  only  a  shattered  and  irregular  crater  ring.  "  The 
great  crater  thus  formed  must  have  had  a  diameter  of  two  or  three 
miles,  and  its  highest  portions  could  have  risen  but  a  few  hundreds 
of  feet  above  the  present  level  of  the  sea."  A  series  of  compara- 
tively quiet  eruptions  must  have  followed,  which  threw  up  a  number 
of  small  cones  within  this  crater  ring.  A  later  stage  was  the  build- 

SEBESI     CHANNEL 


LAKG  X. 


GREAT     CHANNEL 


Encash 


FIG.  99.—  MAP  OF  KRAKATOA,  BEFORE  THE  ERUPTION  OF  1883. 

The  nearly  circular  line  indicates  roughly  the  old  crater  ring. 


ing  up  of  a  cone  (Rakata)  which  rose  on  the  edge  of  the  old  crater 
to  a  height  of  2623  feet  above  the  sea.  An  eruption  occurred  at 
Krakatoa  in  the  year  1680;  after  that  it  remained  for  two  centuries 
perfectly  quiescent  as  a  group  of  islands,  of  which  three  greatly 
exceeded  the  rest  in  size,  the  rim  of  the  old  ruined  crater  being 
indicated  by  two  of  these  and  the  southern  end  of  the  largest 
island,  while  the  greater  part  of  the  last  was  formed  by  the  secondary 
cones,  which,  as  mentioned  above,  had  gradually  accrued.  A  rich 
tropical  vegetation  clothed  the  island  ;  hot  springs  alone  hinted  at 
possible  dangers  in  the  future.  But  in  the  year  1880  all  the  region 
round  began  to  be  frequently  shaken  by  earthquakes.  For  more 


228  THE   STORY  OF  OUR  PLANET. 

than  two  years  no  other  sign  was  afforded  that  mischief  was  threat- 
ening;  then  Sunday  morning,  May  20,  1883,  was  ushered  in  at 
Batavia  and  Buitenzorg  *  by  "  booming  sounds  like  the  firing  of 
artillery."  A  sprinkling  of  ashes  fell  next  day  at  the  latter  town, 
and  in  the  evening  a  column  of  steam  was  seen  issuing  from  Kraka- 
toa.  Next  morning  the  captain  of  a  passing  vessel  observed  that 
the  volcano  was  in  active  eruption,  ejecting  great  clouds  of  vapor 
and  showers  of  dust  and  pumice.  The  former  sometimes  were  shot 
up  to  an  estimated  height  of  seven  miles,  and  volcanic  dust  mounted 
so  far  that  it  drifted  till  it  fell  three  hundred  miles  away. 

For  about  fourteen  weeks  the  eruption  continued  with  varying 
activity,  during  which  time  several  parties  visited  the  island,  and 
made  more  or  less  careful  observations.  An  eruption  thus  com- 
menced might  reasonably  have  been  expected  to  continue  in  a  simi- 
lar phase  of  activity,  and  to  have  ultimately  died  away,  without  any 
marked  change,  except  possibly  the  ejection  of  a  stream  of  lava. 
The  sequel,  however,  was  no  less  unexpected  than  terrible  ;  but 
what  actually  did  happen  can  only  be  inferred,  because  the  island 
itself  was  uninhabited.  Those  nearest  to  the  scene  of  the  eruption, 
whether  on  land  or  on  vessels,  had  enough  to  do  to  save  their  own 
lives — for  many  persons  perished — and  dense  clouds  of  vapor  and 
dust  would  have  baffled  the  most  imperturbable  observer.  The 
phase  of  greatest  violence  set  in  on  Sunday,  August  26.  Soon 
after  midday  it  was  observed  from  passing  ships  that  the  island  had 
disappeared  beneath  a  vast  cloud  of  black  vapor,  the  height  of 
which  was  estimated  at  not  less  than  seventeen  miles ;  frightful 
detonations  resounded  at  intervals,  and  presently,  at  places  full  ten 
miles  away,  a  rain  of  pumice  began  to  fall ;  flashes  of  lightning  rent 
the  masses  of  vapor  for  miles'  round  ;  the  electric  condition  of  the 
atmosphere  was  disturbed,  and  at  a  distance  of  fully  forty  miles 
ghostly  corposants  gleamed  on  the  rigging  of  a  vessel.  Louder  and 
louder  became  the  explosions,  blacker  and  blacker  the  cloud,  yet 
more  widespread  the  darkness,  the  storm,  and  the  waves,  till  the 
paroxysms  culminated  on  August  27,  when  four  explosions  of 
fearful  intensity  shook  earth  and  sea  and  air,  the  third  being  "  far 
the  most  violent  and  productive  of  the  most  widespread  results."f 
The  Titans,  to  use  the  old  Greek  legend,  had  now  succeeded  in 
breaking  prison  ;  the  eruption  evidently  began  to  decline,  and  by 

*  Towns  about  one  hundred  miles  away  from  Krakatoa. 

f  It  occurred  at  10.02  A.  M.  (Krakatoa  time).  The  others  were  5.30,  6.44,  and  at 
10.5-2  A.  M. 


VOLCANIC  ACTION  AND  ITS  EFFECTS.  229 

the  28th  or  2Qth  had  practically  died  away,  though  one  or  two  com- 
paratively insignificant  outbursts  subsequently  occurred. 

This  eruption  had  spread  ruin  and  death  over  many  leagues ;  it 
had  announced  itself,  as  will  be  presently  seen,  to  places  hundreds  of 
miles  distant — nay,  had  even  put  a  girdle  round  the  earth.  At 
Krakatoa  itself,  when  men  once  more  reached  its  shores,  everything 
was  changed.  About  two-thirds  of  the  main  island,  including  all  the 
lower  part  and  the  northern  half  of  Rakata,  were  blown  completely 
away.  This  marginal  cone  had  been  cut  nearly  in  half  vertically, 
the  new  cliff  falling  precipitously  toward  the  center  of  the  crater. 
Where  land  had  been  there  was  now  sea,  in  some  places  more  than 
one  thousand  feet  deep.  The  remaining  part  of  the  island  had 


Vrl.f, 

— \    ,_ 

Straw 

FIG.  100. — SECTION  OF  KRAKATOA,  BEFORE  THE  ERUPTION  OF  1883. 

been  somewhat  increased  by  ejected  materials.  Of  the  other  islands 
and  islets  some  had  disappeared,  some  were  partially  destroyed, 
some  were  enlarged  by  fallen  debris,  while  many  changes  had  taken 
place  in  the  depth  of  the  neighboring  sea  bed.  Much  of  the  ejected 
pumice  was  so  full  of  cavities  as  to  float  upon  the  water.  Here  and 
there  it  formed  great  banks,  which  covered  the  sea  for  miles,  and 
sometimes  rose  four  or  five  feet  above  it,  proving  a  serious  obstacle  to 
navigation.  The  enormous  volumes  of  steam,  mingled  with  mineral 
dust,  which  had  been  discharged  into  the  upper,  air  had  darkened 
the  sky.  At  Batavia,  about  a  hundred  English  miles  away  from  the 
volcano,  it  produced  an  effect  very  similar  to  that  of  one  form  of 
London  fog.  This  began  about  seven  in  the  morning  of  August 
27,  and  gradually  increased  till,  soon  after  ten,  the  light  became 
lurid  and  yellow,  and  lamps  were  required  in  the  houses  ;  then  came 
a  downfall  of  rain,  mingled  with  dust,  and  by  about  half-past  eleven 
the  town  was  in  complete  darkness.  This  lasted  till  about  one 
o'clock,  when  the  sky  began  to  lighten,  the  rain  to  diminish,  till 
about  three  o'clock  it  had  ceased.  At  Buitenzorg  a  similar  darkness 
and  dust-rain  occurred,  but  lasted  there  for  a  shorter  time.  The 
town  is  some  twenty  miles  further  away  from  Krakatoa.  In  many 
places,  at  distances  far  greater,  the  upper  sky  seemed  strangely 


23°  THE   STORY  OF  OUR  PLANET. 

murky,  and  the  sun  assumed  a  green  color.  These  strange  phe- 
nomena were  traced  over  a  broad  zonal  area  of  the  globe,  even  as 
far  as  the  Sandwich  Islands,  while  over  a  yet  wider  area  the  sky 
after  sunset  was  lit  up  by  afterglows  of  extraordinary  beauty. 
These  were  particularly  conspicuous  in  England  during  the  months 
of  November  and  December,  1883.  From  a  careful  collation  and 
comparison  of  the  observations  recorded  it  is  inferred  that  the  great 
dust  cloud  even  made  more  than  the  circuit  of  the  globe.  As  it 
spread  and  dispersed,  the  strangely  tinted  sun— green,  blue,  or  cop- 
per color— was  seen  when  its  denser  parts  were  passing;  by  the 
thinner  the  afterglows  were  produced.  The  finest  materials  prob- 
ably continued  to  float  in  the  atmosphere  for  more  than  a  year. 


FIG.  ioi.— SECTION  OF  KRAKATOA,  AFTER  THE  ERUPTION  OF  1883. 

The  dotted  line  indicates  the  section  of  the  island  before. 

The  height  to  which  this  dust  was  projected  at  first  has  been 
calculated  from  various  data,  with  the  result  that  121,500  feet,  or 
nearly  25  miles,  is  a  very  probable  maximum  estimate,  while  it  is 
not  impossible  that  occasional  fragments  of  larger  size  may  have 
been  shot  up  to  a  yet  greater  height.*  This,  however,  was  not  all. 
Huge  waves,  originating  from  Krakatoa,  traversed  the  sea,  and 
swept  the  coast  bordering  the  Straits  of  Sunda,  destroying  many 
villages  on  the  low-lying  shores  in  Java,  Sumatra,  and  other 
islands.  Buildings  were  sometimes  washed  away  at  the  height  of 
about  50  feet  above  sea  level.  The  water  seems  occasionally  to 
have  risen  still  higher,  and  in  one. exceptional  case  to  have  surged 
up  to  115  feet.  At  Telok  Betong,  in  Sumatra,  a  ship  was  carried 
inland  for  quite  a  mile  and  three-quarters,  and  left  stranded  at  a 
height  of  30  feet  above  the  sea.  The  disturbance  of  the  ocean 
was  traced  —  though  it  speedily  became  unimportant  —  even  as 
far  as  Cape  Horn,  and,  possibly,  to  the  English  Channel.  The 
sounds  of  the  explosion  in  some  cases  were  heard  more  than  2000 
miles  away  ;  the  waves  of  atmospheric  disturbance  encircled  the 
globe,  and  in  one  case  their  passage  was  noted  seven  times  at 

*  Krakatoa  Report,  issued  by  the  Royal  Society,  p.  379. 


VOLCANIC  ACTION  AND  ITS  EFFECTS.  231 

the  same  station.  Still,  vast  as  was  the  quantity  of  material  ejected 
by  Krakatoa,  it  was  on  a  smaller  scale,  in  Professor  Judd's  opinion, 
than  several  other  outbursts  which  have  occurred  in  historic  times. 
"The  great  eruptions  of  Papandayang,  in  Java,  in  1772,  of  Skaptar 
Jokull,  in  Iceland,  in  1783,*  and  of  Tomboro,  in  Sumbawa,  in  1815, 
were  all  accompanied  by  the  extrusion  of  much  larger  quantities  of 
material  than  that  thrown  out  of  Krakatoa  in  1883.  The  special 
feature  of  this  last  outburst  of  the  volcanic  forces  was  the  excess- 
ively violent  though  short  paroxysms  with  which  it  terminated. 
In  the  terrible  character  of  the  sudden  explosions,  which  gave  rise 
to  such  vast  sea  and  air  waves  on  the  morning  of  the  27th  of 
August,  the  eruption  of  Krakatoa  appears  to  have  no  parallel 
among  the  records  of  volcanic  activity.  The  peculiarity  of  the 
phenomena  displayed  during  the  eruption  is,  I  believe,  to  be  ac- 
counted for  by  the  situation  of  the  volcano,  and  its  liability  to  great 
inrushes  of  the  water  of  the  sea,  as  the  evisceration  of  the  crater 
opened  a  way  to  the  volcanic  focus."f 

Since  these  words  were  written  an  outbreak  has  occurred  in  Japan 
which,  though  the  area  of  destruction  was  more  limited,  appears  to 
have  surpassed  even  Krakatoa  in  the  frightful  suddenness  of  the 
catastrophe.  Mr.  Norman,;}:  who  visited  the  spot  shortly  afterward, 
thus  describes  the  scene  of  ruin.  After  a  journey  through  the  for- 
ests which  clothed  the  slopes  of  the  volcanic  mountain  and  prevented 
any  distant  view,  the  travelers  at  last  found  themselves  "  standing 
upon  the  ragged  edge  of  what  was  left  of  the  mountain  of  Bandai- 
san,  after  two-thirds  of  it,  including,  of  course,  the  summit,  had  been 
literally  blown  away  and  spread  over  the  face  of  the  country. 

.  .  The  original  cone  of  the  mountain  had  been  truncated  at  an 
acute  angle  to  its  axis.  .  .  From  our  very  feet  a  precipitous  mud 
slope  falls  away  for  half  a  mile  or  more,  till  it  reaches  the  level. 
At  our  right,  still  below  us,  rises  a  mud  wall  a  mile  long,  also  sloping 
down  to  the  level,  and  behind  it  is  evidently  the  crater ;  .  .  .  but 
before  us  for  five  miles  in  a  straight  line,  and  on  each  side  nearly  as 
far,  is  a  sea  of  congealed  mud,  broken  up  into  ripples  and  waves  and 
great  billows,  and  bearing  upon  its  bosom  ...  a  thousand  huge 
bowlders,  weighing  hundreds  of  tons  apiece."  On  reaching  the 
crater  they  found  it  a  gigantic  caldron,  probably  a  mile  in  width, 
walled  in  with  precipices  of  the  same  mud-like  material ;  from  sev- 

*  Of  which  some  particulars  are  given  below,  p.  248. 

f  Eruption  of  Krakatoa,  Report  of  Committee  of  Royal  Society,  p.  29. 

{  "  The  Real  Japan,"  ch.  x. 


232  THE   STORY  OF  OUR  PLANET. 

eral  orifices  volumes  of  steam  were  being  discharged,  and  when  the 
vapor  cleared  away  for  a  moment  glimpses  of  a  mass  of  boiling  mud 
were  obtained. 

Before  the  explosion  the  mountain  terminated  in  three  peaks. 
The  highest  attained  an  elevation  of  5800  feet;  the  peak  destroyed 
was  the  middle  one,  which  was  rather  smaller  than  the  other  two. 
"  The  explosion  was  caused  by  steam  ;  there  was  neither  fire  nor 
lava  of  any  kind.  It  was,  in  fact,  nothing  more  nor  less  than  a 
gigantic  boiler  explosion.  The  whole  top  and  one  side  of  Sho- 
Bandai-san  had  been  blown  into  the  air  in  a  lateral  direction,  and 
the  earth  of  the  mountain  was  converted  by  the  escaping  steam,  at 
the  moment  of  the  explosion,  into  boiling  mud,  part  of  which  was 
projected  into  the  air  to  fall  a  long  distance,  and  then  take  the  form 
of  an  overflowing  river,  which  rushed  with  vast  rapidity  and  covered 
the  country  from  20  to  150  feet  deep.  Thirty  square  miles  of 
country  were  thus  devastated." 

On  the  slopes  of  the  mountain  and  the  lowlands  which  it  over- 
looked were  fields  and  villages.  Many  lives  were  lost,  but  from  the 
survivors  Mr.  Norman  gathered  some  information,  from  which  an 
idea  may  be  obtained  of  the  main  features  of  .the  catastrophe. 
This  is  a  brief  outline  of  his  narrative:  At  a  few  minutes  past 
eight  o'clock  in  the  morning  a  most  awful  noise  was  heard  by  the 
inhabitants  of  a  village  ten  miles  away  from  the  summit.  Some 
instinctively  took  to  flight,  but  before  a  man  could  run  a  hundred 
and  twenty  yards  the  light  of  day  was  suddenly  changed  into  a 
darkness  exceeding  that  of  midnight ;  a  shower  of  blinding  hot 
ashes  and  sand  came  pouring  down ;  the  ground  was  shaken  with 
earthquakes,  explosion  followed  explosion,  the  last  being  the  most 
violent.  Many  fugitives,  as  well  as  people  in  the  houses,  were  over- 
whelmed in  the  deluge  of  mud,  but  the  spot  where  the  former  perished 
was  only  two  hundred  yards  from  the  village.  From  the  statements 
made  by  those  who  were  so  fortunate  as  to  escape  with  their  lives, 
and  from  his  examination  of  the  ground,  Mr.  Norman  inferred  that 
the  mud  must  have  passed  six  miles  through  the  air  and  then  have 
rushed  along  the  ground  for  four  miles,  in  less  than  five  minutes, 
so  that  "  millions  of  tons  of  boiling  mud  were  hurled  over  the 
country  at  the  rate  of  two  miles  a  minute."  Perhaps  the  velocity 
of  the  mud  torrent  may  be  slightly  overestimated,  but  in  its  awful 
suddenness  this  catastrophe  evidently  has  had  few  equals.  Probably 
the  cone  destroyed  was  largely  composed  of  rather  fine  ash  and 
scoria,  which  was  almost  instantaneously  converted  into  mud  by 


234  THE   STORY  OF  OUR  PLANET. 

the  condensing  steam  and  the  boiling  water  ejected.  The  quantity 
of  water  thus  discharged  must  have  been  enormous. 

Two  episodes  in  the  history  of  Cotopaxi  illustrate  rather  different 
phases  of  volcanic  activity ;  each  is  described  in  Mr.  Whymper's 
great  book  on  the  Ecuadorian  Andes,*  and  of  the  second  he  was  an 
eyewitness.  Cotopaxi  is  situated  about  thirty  geographical  miles 
southeast  of  Quito.  Its  crater  rim  is  about  19,600  feet  above  the 
sea,  for  it  is  the  highest  active  volcano  in  the  world.  Steam  is  con- 
stantly discharged  from  its  crater,  with  occasional  slight  explosions 
which  puff  up  larger  jets ;  volleys  of  dust  occur  at  rather  frequent 
intervals.  Mr.  Whymper,  however,  was  able,  not  only  to  pass  a 
night  on  the  cone  just  below  the  summit,  but  also  to  look  into  the 
crater.  This  is  what  he  saw  :  "  An  amphitheater  2300  feet  in  diam- 
eter from  north  to  south,  and  1650  feet  across  from  east  to  west, 
with  a  rugged  and  irregular  crest,  notched  and  cracked,  surrounded 
by  cliffs,  by  perpendicular,  and  even  overhanging,  precipices,  mixed 
with  steep  slopes — some  bearing  snow,  and  others  apparently  in- 
crusted  with  sulphur.  Cavernous  recesses  belched  forth  smoke ; 
the  sides  of  cracks  and  chasms,  no  more  than  halfway  down,  shone 
with  ruddy  light ;  and  so  it  continued  on  all  sides  right  down 
to  the  bottom,  precipice  alternating  with  slope,  and  the  fiery 
fissures  becoming  more  numerous  as  the  bottom  was  approached. 
At  the  bottom,  probably  1200  feet  below  us,  and  toward  the 
center,  there  was  a  rudely  circular  spot,  about  one-tenth  of  the 
diameter  of  the  crater,  the  pipe  of  the  volcano,  its  channel  of  com- 
munication with  lower  regions,  filled  with  incandescent,  if  not  molten, 
lava,  glowing  and  burning;  with  flames  traveling  to  and  fro  over  its 
surface,  and  scintillations  scattering  as  from  a  wood  fire ;  lighted  by 
tongues  of  flickering  flame,  which  issued  from  the  cracks  in  the 
surrounding  slopes.  At  intervals  of  about  half  an  hour  the  volcano 
regularly  blew  off  steam.  It  arose  in  jets  with  great  violence  from 
the  bottom  of  the  crater,  and  boiled  over  the  lip,  continually  envel- 
oping us.  The  noise  on  these  occasions  resembled  that  which  we 
hear  when  a  large  ocean  steamer  is  blowing  off  steam." 

But  at  any  moment  Cotopaxi  may  pass  into  a  more  violent  phase 
of  activity.  One  of  these  occurred  in  1877.  First  a  great  column 
of  dust  was  ejected,  followed  next  day  by  a  second  mass,  which 
drifted  high  in  air  above  Quito,  so  that  midday  was  dark  as  night. 
The  next  morning  the  summit  of  the  volcano  was  clear,  but  about 

"  Travels  in  the  Great  Andes  of  the  Equator,"  ch.  vi.,  etc. 


VOLCANIC  ACTlOff  AND  ITS  EFFECTS. 


235 


FIG.  103. — DUST  CLOUD  FROM 
COTOPAXI 


ten  o'clock  some  people  who  were 
looking  at  it  "  saw  molten  lava  pour- 
ing through  the  gaps  and  notches 
in  the  lip  of  the  crater,  bubbling 
and  smoking,  so  they  described  it, 
like  the  froth  of  a  pot  that  suddenly 
boils  over."  After  this  what  ensued 
upon  the  mountain  no  man  could 
see,  for  in  a  few  minutes  the  whole 
of  it  was  enveloped  in  smoke  and 
steam,  and  became  invisible,  "  but 

out  of  the  darkness  a  moaning  noise  arose,  which  grew  into  a  roar, 
and  a  deluge  of  water,  blocks  of  ice,  mud,  and  rock  rushed  down, 
sweeping  away  everything  that  lay  in  its  course,  and  leaving  a  des- 
ert in  its  rear."  The  molten  matter,  as  Mr.  Whymper  points  out, 
which  overflowed  from  the  crater,  and  fell  in  streams  or  cascades 
upon  the  surrounding  slopes  of  snow  and  ice,  must  often  have  been 
sent  flying  into  the  air  in  shattered  fragments  and  splashes  by  the 
sudden  development  of  steam,  and  "  portions  of  the  glaciers,  un- 
cemented  from  their  attachments  by  the  enormous  augmentation  of 
heat,  slipped  away  bodily,  and  partly  rolling,  partly  borne  by  the 
growing  floods,  arrived  at  the  bottom  a  mass  of  shattered  blocks." 
The  other  episode  illustrates  a  milder  phase  of  the  mountain's 
activity.  Mr.  Whymper  was  making  his  second  ascent  of  Chimbo- 
razo.  The  sky  was  bright,  and  the  cone  of  Cotopaxi,  sixty  miles 
away,  stood  up  clear  in  the  dawning  light.  The  great  volcano  was 
unusually  tranquil,  not  a  sign  of  smoke  rose  from  its  crater.  "  At 
5.40  A.  M.  two  puffs  of  steam  were  emitted,  and  then  there  was  a 
pause.  At  5.45  a  column  of  inky  blackness  began  to  issue,  and 
went  up  straight  into  the  air  with  such  prodigious  velocity  that  in 
less  than  a  minute  it  had  risen  20,000  feet  above  the  rim  of  the 
crater."  At  this  height  it  appeared  to  be  caught  by  a  powerful 
current  of  air  from  the  east,  and  was  "  rapidly  borne  toward  the 


236  THE   SI  CRY  OF  OUR  PLANET. 

Pacific;  remaining  intensely  black,  seeming  to  spread  very 
slightly  "  ;  then  it  was  caught  by  another  current  from  the  north, 
and  drifted  toward  Chimborazo,  spreading  out  rapidly.  When  the 
party  reached  the  summit,  though  the  cloud  was  then  hovering 
overhead,  the  snows  were  clean,  but  about  ten  minutes  afterward 
the  dust  began  to  fall,  and  in  the  course  of  an  hour  gave  the  white 
dome  the  aspect  of  a  plowed  field.  In  Mr.  Whymper's  words: 
"  It  filled  our  eyes  and  nostrils,  rendered  eating  and  drinking  im- 


FlG.    104. — VESUVIUS,    FROM   THE   BAY    OF   NAPLES. 

possible,  and  at  last  reduced  us  to  breathing  through  handker- 
chiefs."* The  dust  had  occupied  some  7^  hours  on  its  aerial 
journey. 

The  history  of  Vesuvius,  more  notably  in  some  ways  than  that 
of  Krakatoa,  affords  an  instance  of  long  quiescence  followed  by  a 
sudden  and  destructive  awakening.  The  mountain,  about  nineteen 
centuries  since,  exhibited  an  outline  widely  different  from  its 
present  one.  It  terminated  in  a  broad  crater,  inclosed  by  steep 
walls,  comparable  with  that  of  Astroni,f  but  only  about  500  feet 
lower  than  the  height  of  the  present  summit.  Scoria  and  lava  in- 
dicated the  origin  of  this  huge  natural  amphitheater ;  but  not  so 

*  The  dust  consists  of  fragments  of  transparent  glass  and  minerals  (felspar  and  augite), 
with  occasional  bits  of  dark  scoria.  Many  of  these  range  from  .003  to  .004  of  an  inch  ; 
from  this  they  go  to  the  finest  dust  ;  larger  fragments  are  rare,  .01  being  about  the  maxi- 
mum size. — "  Proc.  Royal  Soc.,"  xxxvii.  p.  123. 

f  Probably  it  was  about  a  mile  in  diameter. — Phillips,  "  Vesuvius,"  p.  176. 


VOLCANIC  ACTION  AND  ITS  EFFECTS.  237 

much  as  a  jet  of  steam  or  spring  of  boiling  mud  issued  from  any 
fissure  to  intimate,  as  at  the  Solfatara,  that  mischief  might  be  still 
a-brewing.  The  volcanic  energy  appeared  to  have  been  completely 
exhausted  ;  the  floor  of  the  crater  was  overgrown  with  dense  vege- 
tation, its  walls  were  festooned  by  wild  vines.  This  period  of 
quiescence  continued  for  one  knows  not  how  many  centuries.  The 
memory  of  a  volcanic  outburst  from  Vesuvius,  if  it  had  not  totally 
faded  away,  was  only  preserved  as  a  dim  and  uncertain  tradition. 


FIG.  105.— OUTLINE  OF  MONTE  SOMMA. 

This  outline,  sketched  from  the  north,  shows  the  present  rim  of  Monte  Somma  and  the  probable  shape 
of  Vesuvius  prior  to  A.D.  79.     The  cone  is  just  visible  on  the  spot  marked  A. 

Then  the  district  began  to  be  shaken  by  earthquakes  ;  for  sixteen 
years  these  continued,  till  at  last,  in  the  year  79  A.  D.,  on  the  night 
of  August  24,  they  became  so  violent  that  the  whole  country 
seemed  "  to  reel  and  totter."  Next  day,  soon  after  noon,  a  huge 
black  cloud  uprose  from  the  crater  of  Vesuvius.  An  eyewitness* 
compares  its  shape  to  a  stone-pine,  for,  as  he  said,  "  it  shot  up  to  a 
great  height  in  the  form  of  a  trunk,  which  extended  itself  at  the 
top  into  a  sort  of  branches.  .  .  It  appeared  sometimes  bright, 
sometimes  dark  and  spotted,  as  it  was  more  or  less  impregnated 
with  earth  and  cinders."  Presently  a  continuous  shower  of  dust 
and  ash  and  blocks  of  stone  began  to  fall  over  all  the  country  round. 
As  night  came  on,  the  darkness  was  illumined  with  the  gleam  of  light- 
ning and  the  glare  of  the  volcano,  while  the  air  quivered  with  the 
reports  of  explosions,  the  sea  was  strangely  agitated,  and  the  ground 
shuddered  with  earthquake  shocks.  The  esuption  seems  to  have 

*The  younger  Pliny — quoted  by  Professor  Phillips,  "  Vesuvius,"  p.  15. 


238  THE   STORY  OF  OUR  PLANET. 

continued  in  full  violence  for  at  least  another  day,  but  after  that  it 
subsided.  It  had  wrought  no  small  change  in  the  mountain  ;  half 
the  old  crater  wall  had  been  blown  away  and  had  been  strewn  in 
fragments  over  the  slopes  and  lowlands  all  around ;  the  remnant 
still  encircles  the  northern  side  of  the  present  cone,  and  bears  the 
name  of  Monte  Somma.  As  at  that  time  probably  a  central  cone 
had  not  been  formed,  the  ruined  walls  would  overhang  a  bowl-like 
gulf.  Herculaneum,  Stabiae,  and  Pompeii  had  disappeared,  the 
first  beneath  a  thick  mass  of  mud,  the  last  under  a  cloak  of  scoria  ; 
to  beyond  Capo  di  Miseno,  fifteen  miles  away  from  the  crater,  the 
whole  country  "  was  covered  with  white  ashes  as  with  a  deep  snow." 

Since  then  the  volcano  has  been  often  active,  but  for  nearly  six- 
teen centuries  its  eruptions,  though  not  unfrequent,  appear  gener- 
ally not  to  have  been  violent.  So  far  as  can  be  inferred  from  a 
rather  confused  account  written  early  in  the  seventeenth  century,  a 
central  cone  had  not  yet  been  thrown  up.  But  in  1631  another  out- 
burst occurred,  only  less  destructive  than  that  of  79.  As  before, 
large  quantities  of  scoria  were  discharged,  but  on  this  occasion 
streams  of  lava  poured  down  the  flanks  of  the  mountain,  and 
reached  the  sea  "  at  twelve  or  thirteen  points."  By  these  Resina, 
Granatello,  and  Torre  del  Greco  were  partly  destroyed,  and  the  loss 
of  life  is  put  as  high  as  18,000.  Since  then  Vesuvius  has  seldom 
rested.  A  central  cone  seems  to  have  been  thrown  up  by  the  last- 
named  eruption;  this  has  been  augmented,  truncated,  and  built  up 
again,  so  that  for  some  two  centuries  the  aspect  of  the  mountain 
has  not  been  materially  changed.  Vesuvius  thus  affords  an  example 
of  a  volcano,  comparatively  insulated  in  position,  dominating  the 
country  round,  like  Etna  or  Teneriffe,  which  remained  quiescent 
for  an  unknown  number  of  centuries,  then  woke  up,  truly  like  a 
giant  refreshed,  to  a  new  phase  of  destructive  activity. 

Submarine  volcanic  eruptions,  for  various  obvious  reasons, are  more 
seldom  observed,  and  less  perfectly  recorded.  But  the  well-known 
case  of  Graham  Island  may  be  quoted  as  an  example  which,  no 
doubt, is  not  very  exceptional.  The  site  of  Graham  Island  was  about 
30  miles  S.W.  of  Sciacca,  in  Sicily,  and  33  miles  N.E.  of  the  island 
of  Pantellaria.*  The  general  depth  of  the  water  hereabouts,  prior 
to  1831,  was  rather  more  than  a  hundred  fathoms.  "  On  June  28, 
about  a  fortnight  before  the  eruption  was  visible,  Sir  Pulteney  Mal- 
colm, in  passing  over  the  spot  in  his  ship,  felt  the  shocks  of  an  carth- 
• 

*Lyell,  "  Principles  of  Geology,"  ch.  xxvii. 


VOLCANIC  ACTION  AND  ITS  EFFECTS.  239 

quake,  as  if  he  had  struck  on  a  sand  bank."  The  adjoining  coast  of 
Sicily  was  also  disturbed.  Nearly  a  fortnight  later  the  captain  of 
a  Sicilian  vessel  reported  that  he  had  observed  in  passing  the  water 
spouting  up  to  a  height  of  60  feet,  followed  by  a  dense  cloud  of 
steam,  which  rose  1800  feet  above  the  sea.  On  July  18  he  passed 
this  spot  as  he  returned,  and  found  there  an  "  island  12  feet 
high,  with  a  crater  in  its  center,  ejecting  volcanic  matter  and  im- 
mense columns  of  vapor,  the  sea  around  being  covered  with  floating 
cinders  and  dead  fish.  The  scoriae  were  of  a  chocolate  color,  and 
the  water  which  boiled  in  the  circular  basin  was  of  a  dingy  red." 
The  eruption  continued  with  great  violence  to  the  end  of  the  same 
month,  at  which  time  the  island  was  visited  by  more  than  one 
person.  "  It  was  then  from  50  to  90  feet  in  height,  and  three- 
quarters  of  a  mile  in  circumference.  By  August  4  it  became, 
according  to  some  accounts,  about  200  feet  high,  and  3  miles  in 
circumference  ;  after  which  it  began  to  diminish  in  size  by  the  action 
-of  the  waves,  and  was  only  2  miles  round  on  August  25  ;  and 
on  September  3,  when  it  was  carefully  examined  by  Captain  Wode- 
house,»only  three-fifths  of  a  mile  in  circumference,  its  greatest  height 
being  then  107  feet.  At  this  time  the  crater  was  about  780  feet  in 
circumference."  The  island  is  described  as  consisting  entirely  of 
scoriae  and  pumiceous  materials,  except  fora  few  fragments  of  dol- 
omitic  limestone,  which  also  had  been  ejected,  hardly  anything 
exceeding  a  foot  in  diameter.  During  the  month  of  August  the 
water  had  been  seen  to  boil  up,  and  a  column  of  steam  to  be 
ejected,  on  the  S.W.  side  of  the  island,  as  if  a  second  and  lateral 
vent  had  opened  out  in  the  new  volcano.  By  the  month  of  October 
the  island  had  been  almost  washed  away,  and  not  long  after  that 
it  disappeared  ;  but  the  site  was  marked  by  a  dangerous  reef,  oval 
in  form,  and  about  three-fifths  of  a  mile  in  extent.  "  In  the  center 
was  a  black  rock,  of  the  diameter  of  about  26  fathoms  from 
9  to  1 1  feet  under  water,  and  round  the  rock  were  banks  of 
black  volcanic  stones  and  loose  sand.  At  a  distance  of  60  fathoms 
from  this  central  mass  the  depth  increased  rapidly.  There  was  also 
a  second  shoal  at  the  distance  of  450  feet  S.W.  of  the  great  reef, 
with  15  feet  of  water  over  it,  also  composed  of  rock,  surrounded 
by  deep  sea.  We  can  scarcely  doubt  that  the  rock  in  the  middle  of 
the  larger  reef  is  solid  lava^and  that  the  second  shoal  marks  the 
site  of  the  submarine  eruption  observed  in  August,  1831,  to  the  S.W. 
of  the  island."  As  Sir  C.  Lyell  observes,  although  no  lava  appears 
to  have  risen  up  above  the  level  of  the  waves,  yet  molten  rock  may 


240  THE   STORY  OF  OUR  PLANET. 

have  flowed  from  the  flank  or  base  of  the  cone,  and  spread  out  in  a 
broad  sheet  over  the  bottom  of  the  sea. 

Thus  Graham  Island  indicates — and  the  example  is  only  one  of  a 
group — how  the  continuity  of  submarine  deposits,  whether  sands  or 
clays  or  limestones,  may  be  suddenly  interrupted  by  the  incoming 
of  beds  of  volcanic  ashes,  and  even  by  flows  of  lava.  Instances  of 
this  not  unfrequently  occur.  For  example,  in  the  limestone  district 
of  Derbyshire  we  find  that  this  rock  in  one  place  changes  abruptly 
in  an  upward  direction  into  an  ashy  deposit,  in  which  marine  shells 
occur,  indicating  that  the  denizens  of  the  sea  bed  probably  suffered 
the  same  fate  as  the  inhabitants  of  Pompeii ;  in  another  place  the 
limestone  is  covered  by  a  chocolate-colored  volcanic  mud,  and  over 
each  of  these  deposits  comes  a  sheet  of  lava,  which  obviously  must 
have  flowed  on  the  old  sea  bed.  The  very  summit  of  Snowdon 
itself  bears  testimony  to  a  similar  condition  of  things,  for  it  is 
formed  of  an  ashy  rock  which  is  crowded  with  the  impressions  of 
seashells. 

The  instances  of  volcanic  eruptions  described  above  indicate  that 
they  are  accompanied  by  explosive  phenomena,  often  of  tremendous 
violence,  and  that  the  result  of  these  not  seldom  is  destructive.  It 
is  also  constructive.  In  many  cases  the  cone  itself  obviously  is  built 
up  by  the  ejected  material ;  the  whole  mound  of  Monte  Nuovo  and 
the  central  hill  of  Vesuvius  have  both  been  formed  during  the  last 
few  centuries.  By  the  examination  even  of  volcanoes  still  active 
we  are  led  to  the  conclusion  that  they  are  at  least  very  largely  the 
product  of  erupted  material,  and  this  is  strengthened,  as  will  pres- 
ently be  seen,  by  the  study  of  the  structure  of  those  which  have 
become  extinct.  But  before  proceeding  to  this  anatomical  investi- 
gation, as  it  may  be  called,  we  may  do  well  to  notice  one  or  two 
phenomena  connected,  more  especially,  with  the  discharge  of  lava. 
This,  however,  does  not  always  occur.  Craters  there  are,  like  some 
of  those  in  the  volcanic  district  of  the  Eifel,  from  which  no  lava  has 
ever  flowed,  and  sometimes  no  large  quantity  of  ash  and  scoria  has 
been  ejected.  Such  are  the  craters — now  occupied  by  small  lakes — 
of  the  Gemunder  Maar  or  the  Weinfelder  Maar,  near  Daun,  or  the 
Pulver  Maar,  near  Gillenfeld,  where  in  the  discharged  materials  bits 
of  slate  (the  country  rock)  are  almost  as  abundant  as  scoria.  The 
vapors  imprisoned  beneath  the  surface  appear  to  have  blown  a  small 
hole  in  the  earth's  crust,  from  which  a  few  showers  of  volcanic  dust 
and  ash,  mingled  with  shattered  sedimentary  rock,  have  been  thrown 
out.  Evidently  not  one  of  these  craters  can  have  remained  active 


VOLCANIC  ACTION  AND    ITS  EFFECTS.  241 

for  any  long  time,  for  otherwise  a  larger  amount  of  material  would 
have  been  ejected  ;  they  were  very  probably,  like  Monte  Nuovo,  the 
outcome  of  a  single  eruption.  But  lava,  as  a  general  rule,  is  dis- 
charged, in  the  course  of  an  eruption,  usually  rather  late  in  its 
history.  Sometimes,  as  was  described  in  the  case  of  Cotopaxi,  and 
has  happened  more  than  once  in  Vesuvius,  the  lava  wells  up  in  the 
crater,  like  water  from  a  spring,  and  overflows  the  rim,  streaming 
down  the  outer  slopes  in  glowing  torrents,  or  occasionally  in  one 
unbroken  sheet  of  molten  rock.  More  often  the  walls  of  the  crater 
are  ruptured  by  the  pressure  of  the  rising  mass,  and  the  incandescent 
material  rushes  out  from  the  fissure.  Not  less  frequently  cracks 
open  out  in  the  mountain  itself,  through  which  the  lava  escapes, 
as  by  a  lateral  passage,  before  reaching  the  bottom  of  the  crater, 
and  issues  on  the  slopes  some  distance  below  the  base  of  the  actual 
cone.  Indications  of  the  cracked  and  often  tottering  condition  of 
many  volcanic  mountains  are  afforded  by  the  parasitic  cones,  which 
are  frequently  numerous.  So  many  have  been  counted  on  Etna 
that,  on  a  small  scale  model,  the  volcano  seems  to  be  suffering  from 
a  bad  outbreak  of  boils.  On  Vesuvius  an  interesting  example  of 
one  of  these  emissaries  of  a  lava  flow  can  be  readily  examined. 
The  outbreak  occurred  during  the  eruption  of  i86i,on  the  southern 
side  of  the  mountain,  some  considerable  distance  below  the  base  of 
the  actual  cone.  The  slope  is  interrupted  by  a  shallow  trench,  hardly 
deep  enough  to  be  called  a  glen,  which  is  terminated  at  its  upper 
end  by  a  cliff  perhaps  fifty  feet  high.  This  affords  a  section  of 
bedded  volcanic  materials  of  a  yellowish-gray  color — finer  and  more 
regularly  stratified  in  the  upper  part,  coarser  and  more  irregular  in 
the  lower.  The  cliff  is  split  by  a  crack,  running  vertically  upward, 
and  narrowing  in  that  direction,  till  it  is  lost  to  sight  in  the  finer  and 
more  incoherent  material. 

At  the  bottom,  where  it  is  widest,  the  surface  of  a  wedge-like 
mass  of  lava  is  first  exposed,  a  mere  chine  of  rough  rock.  The  bed 
of  the  gully,  a  short  distance  further  down,  is  choked  by  a  low  mon- 
ticule of  scoria,  forming  a  double  crater,  the  upper  and  larger  basin, 
which  is  in  shape  an  oval,  being  about  sixty  yards  long  and  thirty 
wide ;  from  this  a  line  of  eight  other  small  and  low  cones  can  be 
followed  down  the  hillside,  the  lava  flow  broadening  out  from  below 
the  base  of  the  last.  These  craters  evidently  mark  the  course  of  a 
fissure  from  which  the  lava  has  issued  and  at  close  intervals  has 
"  blown  off  steam"  as  the  pressure  was  removed  from  which  it  had 
suffered  during  its  subterranean  course. 


242  THE   STORY  OF  OUR  PLANET. 

One  of  the  most  remarkable  instances  on  record  of  the  under- 
ground passage  of  lava  happened  in  the  Sandwich  Islands  in  the 
year  1840*  in  connection  with  a  threatened  eruption  of  Kilauea. 
In  the  earlier  part  of  the  summer  the  molten  lava  had  welled  up 
high  in  the  crater,  but  about  the  month  of  June  it  came  to  a  stand- 
still, after  which  its  surface  began  to  sink.  The  cause  of  this 
change  was  speedily  made  apparent.  Six  miles  away,  at  the  bot- 
tom of  an  old  wooded  crater  called  Arare  a  glowing  mass  became 
visible,  which,  however,  did  not  overflow  or  even  fill  up  the  crater. 
Next,  a  mile  or  two  down  the  slope,  a  stream  of  lava  broke  forth 
from  the  ground,  and,  spreading  out  as  it  flowed,  covered  an  area 
of  about  fifty  acres.  After  this,  yet  some  miles  lower  down,  the 
lava  again  appeared  at  the  bottom  of  another  old  wooded  crater, 
which  it  filled  up,  but  without  further  overflow.  Lastly,  at  a 
distance  of  twenty-seven  miles  from  Kilauea,  and  1244  feet  above  the 
sea,  the  glowing  stream  finally  emerged  from  the  earth,  and  ran  for 
twelve  miles  further,  till  it  poured  down  a  cliff  fifty  feet  high,  and 
its  further  course  was  arrested  by  the  ocean.  As  we  cannot  sup- 
pose the  existence  of  a  line  of  caves  or  subterranean  channels — 
for  by  what  means  could  they  be  excavated  or  even  kept  open? 
— this  mass  of  molten  material  must  have  forced  its  way  under 
ground  from  some  rent  which  had  been  made  in  the  pipe  lead- 
ing to  the  crater  of  Kilauea.  As  the  lava  was  sufficiently  liquid 
on  emerging  from  a  subterranean  journey  of  twenty-seven  miles  to 
run  for  twelve  more  in  the  open  air,  it  must  have  been  raised  orig- 
inally to  a  temperature  far  above  the  melting  point  of  the  ma- 
terial. Probably  the  three  minor  outbreaks  which  marked  the  line 
of  its  passage  underground  were  not  on  the  actual  course  of  the 
main  stream,  but  indicated  the  ends  of  small  offshoots  from  it 
which  had  forced  their  way  into  lateral  fissures  along  lines  of 
weakness. 

As  lava  flows  onward  its  surface  is  overhung  by  a  cloud  of  steam, 
disengaged  from  the  glowing  mass.  The  discharge  sometimes  con- 
tinues for  weeks  after  motion  has  ceased  and  the  mass  has  appa- 
rently cooled.  This,  however,  is  generally  a  rather  slow  process. 
Lava  is  a  very  bad  conductor,  so  that  when  a  crust  has  once  formed 
on  its  surface  heat  escapes  from  the  interior  very  gradually.  Even 
after  a  lapse  of  three  or  four  years  a  lava  stream  may  often  be  seen 

*Sir  C.  Lyell,  "Elements  of  Geology,"  ch.  xxix.;  J.  D.  Dana,  "Characteristics  of 
Volcanoes, "p.  61. 


VOLCANIC  ACTION  AND  ITS  EFFECTS.  243 

to  steam  in  many  places  after  a  shower  of  rain,  showing  that  the 
lower  part  of  the  mass  is  still  warm. 

Hardly  anything  is  known  as  to  the  temperature  of  lavas  when 
they  emerge  from  a  volcano,  but  this  generally  must  be  consider- 
ably above  the  actual  melting  point  of  the  rock.  Even  as  to  that 
our  information  is  still  very  imperfect.  Obviously  its  exact  value 
must  depend,  in  the  first  instance,  on  the  chemical  composition  of 
the  mass.  But  it  is  also  affected,  even  in  the  same  rock,  by  the 
quantity  of  water  present ;  for  this,  as  will  be  more  fully  indicated 
in  a  later  chapter,  has  a  marked  effect  in  facilitating  fusion.  At 
Vesuvius,  on  one  occasion,  the  temperature  of  lava  still  in  motion 
was  found  to  be  as  low  as  1228°  F.,  while  a  piece  of  silver  wire  was 
quickly  melted  on  another  occasion,  and  copper  on  a  third.  These 
facts  signify  temperatures  exceeding  1800°  F.  and  2204°  F.  respec- 
tively. Probably,  as  a  rough  estimate,  the  temperature  of  lava 
when  first  emitted,  as  a  rule,  is  not  below  2000°  F.* 

The  aspect  of  a  lava  stream  varies  much,  in  accordance,  partly, 
with  its  chemical  composition.  It  may  be  glassy,  slaggy,  or 
"  stony  ";  it  may  be  smooth  or  rough  in  texture ;  it  may  be  solid 
or  full  of  cavities,  which  may  be  small  or  comparatively  large, 
in  shape  regular  or  comparatively  irregular.  In  color  it  may 
be  light  grayish,  yellowish,  or  greenish — or  dark  to  almost  black. 
Lavas  allied  to  basalt  are  perhaps,  on  the  whole,  the  commoner. 
These  also  differ  much  in  appearance,  though  not  in  color. 
The  surface  of  some  streams  is  comparatively  smooth  and  -slaggy- 
looking,  wrinkled  and  ropy,  all  in  folds  and  rolls  and  coils,  as 
if  from  the  slow  flowing  of  a  viscous  mass  ;  while  the  surface  of 
others  is  rough  and  jagged  and  extremely  irregular,  like  a  heap  of 
cinders  or  the  top  of  a  wall  built  with  "  clinkers."  Both  kinds  are 
common  in  the  Sandwich  Islands,  where  they  have  been  distin- 
guished by  native  names.  Both  may  have  been  ejected  by  the 
same  volcano  at  different  dates,  as  may  be  seen  on  Vesuvius. 

More  than  one  of  the  instances  of  volcanic  activity  described 
above  makes  it  clear  that  the  materials  ejected  from  a  volcanic 
orifice  build  up  the  cone  with  its  crater.  Supposing  no  destructive 
effects  from  explosions  of  more  than  usual  violence,  part  of  each 
volley  of  scoria,  after  a  path  of  greater  or  less  length  through  the 
air,  falls  down  on  the  outer  slope  of  the  heap  already  accumulated. 

*  The  melting  point  of  pure  iron  is  estimated  at  about  1600°  F.,  of  silver  about 
1873°  FM  of  gold  2015°  F.  The  lava  in  the  crater  of  Kilauea  is  often  observed  to  be  at 
a  white  heat,  which  indicates  a  temperature  of  about  2400°  F, 


244  THE    STORY  OF  OUR   PLANET. 

Some  fragments  lie  where  they  have  dropped,  some  half-molten 
splashes  may  even  aid  in  cementing  the  mass  together,  but  other 
fragments  roll  for  some  distance  down  the  slope  of  the  cone, 
becoming  rudely  sorted  out  by  size  and  weight,  as  when  gravel  is 
"  tipped  "  down  a  bank.  Thus  the  cone  assumes  a  roughly  stratified 
structure,  and  as  it  increases  in  dimensions,  vertically  and  laterally, 
the  slope  of  its  exterior  probably  diminishes.  The  mass  may  be 
strengthened  by  the  occasional  overflow  of  lava  from  the  crater,  or 
from  rifts  in  its  side.  In  the  latter  the  molten  matter  solidifies, 
forming  what  are  called  dykes,  and  helps  in  binding  the  whole 
together.  Cones  formed  entirely  of  solid  lava  are  not  unknown, 
but  these  are  generally  small  and  steep-sided,  and  have  been  built 
by  up-squirted  stuff  as  vapor  is  escaping  from  the  surface  of  a  large 
stream  of  very  liquid  lava. 

That  a  volcano  is  reared  practically  by  one  architect,  that  the 
whole  cone  and  the  mountain  proper  are  formed  by  the  ejected 
material,  is  now  generally  admitted.  But  this  opinion  was  not 
always  favorably  regarded.  Before  the  days  of  Scrope  and  Lyell 
the  ejected  materials  were  generally  supposed  to  play  a  sub-- 
ordinate  part,  and  a  volcanic  mountain  was  held  to  be  largely  due 
to  the  upheaval  of  the  strata  of  the  earth's  crust  in  a  conical  form 
around  the  orifice.  In  this  hypothesis  obvious  difficulties  existed, 
such  as  that  of  understanding  how  beds  thus  uplifted  could  main- 
tain their  position  as  soon  as  the  imprisoned  vapors  and  lava  had 
escaped  from  beneath  ;  but  as  a  lengthy  discussion  of  an  idea  which 
always  owed  more  to  fancy  than  to  fact  is  unnecessary  at  the 
present  day,  it  may  suffice  to  give  some  account  of  dissected 
volcanoes  in  order  to  show  that  no  such  hypothesis  is  in  accord 
with  the  facts  observed.  "  Subjects,"  to  use  the  technical  term, 
prepared  by  Nature  to  illustrate  the  pathology  of  volcanoes  can  be 
found  in  some  parts  of  the  British  Isles,  or  at  no  very  great  dis- 
tance from  their  shores.  Though  no  craters  remain  in  the  former 
region,  these  are  abundant  in  the  Eifel,  or  still  better  in  Auvcrgne, 
where  their  condition  is  so  perfect  that  it  is  sometimes  hard  to 
believe  that  eruptions  have  not  occurred  within  the  period  over 
which  history  extends.*  The  vent,  indeed,  is  tightly  sealed  ;  grass 

*  Passages  occur  in  the  writings  of  Sidonius  Apollinaris,  Bishop  of  Clermont  circa 
460  A.  D.,  and  Alcimus  Avitus,  Archbishop  of  Vienne,  born  about  the  middle  of  the  same 
century,  which,  if  not  merely  bombast,  imply  lhat  there  were  some  eruptions,  possibly 
but  slight,  in  Central  France  about  that  time.  Most  of  the  craters,  however,  are 
undoubtedly  older  than  the  historic  ages.  (See  Geological  Magazine,  1865,  p.  241.) 


VOLCANIC  ACTION  AND  ITS  EFFECTS. 


245 


covers  the  slopes  of  cone  and  bowl  ;  cattle  graze  peacefully,  as  the 
scoria  still  sometimes  grates  beneath  their  tread,  on  the  spots  where 
glowing  ashes  once  fell  like  rain,  or  clamber  over  the  rugged  sur- 
face of  the  lava  streams  to  seek  the  herbage  which  now  sprouts  from 
its  cracks.  Here  and  there,  as  in  the  Puy  de  las  Solas  and  Puy  de 


FIG.  106.— BREACHED  CRATERS,  AUVERGNE. 

la  Vache,  the  cinder  cones  have  been  burst  by  the  pressure  of  the 
lava  swelling  up  within  so  as  to  afford  opportunities  of  ascertaining 
their  structure.  In  many  other  places  partially  destroyed  cones  are 
common.  Always  they  consist  of  ejected  materials,  and  exhibit  a 
rude  stratification,  as  above  described.*  In  a  more  advanced  state 
of  ruin  the  crater  has  entirely  disappeared,  and  the  cone  has  been 
reduced  to  a  stump,  consisting  often  of  a  central  plug  of  lava,  which 

*  Occasionally  the  beds  in  the  inner  part  of  the  crater  dip  inward  or  in  the  reverse 
direction  to  those  which  make  up  the  greater  part  of  the  cone.  These  would  be  formed 
as  the  eruption  was  subsiding,  and  the  explosive  force  no  longer  sufficed  to  heave  the 
materials  beyond  the  rim  of  the  crater. 


246  THE   STOAT  Of  OUR  PLANET. 

now  forms  the  culminating  point  of  the  hill,  while  masses  of  scoria 
still  cling  to  its  flanks,  sometimes  in  considerable  quantities,  some- 
times merely  in  fragmental  patches.  This,  in  the  opinion  of  some 
geologists,  is  the  history  of  Arthur's  Seat,  near  Edinburgh.  It  is 
generally  admitted  to  be  true  of  many  "  laws  "  in  Scotland,  and 
of  not  a  few  hills  in  Auvergne,  the  Eifel  and  other  old  volcanic 
districts ;  also  in  the  central  valley  of  Scotland  many  volcanic 
"  necks  "  may  be  seen — often  on  quite  a  small  scale — representing 
a  still  more  advanced  stage  of  dissection.  Sometimes  the  con- 
tinuity of  the  stratified  beds  in  the  face  of  a  cliff  is  sharply  inter- 
rupted by  a  dark  mass  which,  on  closer  examination,  proves  to  be 
formed  of  volcanic  material,  mingled  occasionally  with  fragments  of 
sedimentary  rock,  or  seamed  with  a  dyke.  Sometimes  on  the  sea- 
shore a  similar  dark  mass,  more  or  less  circular  in  form,  interrupts, 
like  an  island,  the  uniform  lines  of  the  outcropping  edges  of  the 
strata,  and  is  found  to  have  a  similar  composition.  The  one  is  a 
vertical,  the  other  is  a  horizontal  section  of  a  volcanic  neck.  The 
Fifeshire  coast  affords  many  examples,  in  the  neighborhood  of 
Burntisland,  or  between  Elie  and  St.  Monance.  The  noted  Rock* 
and  Spindle,  near  St.  Andrews,  is  a  fragment  of  a  volcanic  neck,  the 
former  being  a  mass  of  volcanic  agglomerate,  the  latter  a  section 
of  an  intrusive  mass  of  basalt,  more  or  less  cylindrical  in  shape, 
which  has  set  up  a  radiating  columnar  structure.  So,  as  the 
geologist's  eye  becomes  trained,  he  is  able  to  pass  onward  from 
these  more  conspicuous  and  obvious  examples  to  discover  in  the 
granitic  hills  of  Mull,  and  the  dark  masses  which  form  the  wild 
crags  of  "  the  Cuchullins,"  in  Skye,  proofs  that  these  are  the  last 
remnants  of  volcanic  mountains  which  in  their  day — and  that  is 
comparatively  a  late  one  in  the  long  annals  of  geology — were  no 
unworthy  rivals  of  Etna  or  of  Teneriffe ;  nay,  even  Ben  Nevis  itself 
may  be  only  the  time-worn  fragment  of  a  volcano  which  became 
extinct  at  a  far  earlier  epoch. 

In  no  case  can  evidence  be  obtained  which  lends  any  real  support 
to  the  notion  that  the  upheaval  of  stratified  rock  has  played  an 
important  part  in  the  formation  of  a  volcanic  mountain.  So  far 
from  this,  it.  all  tends  rather  to  the  contrary  opinion,  for  the  strata 
are  not  seldom  found  to  be  somewhat  bent  in  a  downward  direction 
near  to  a  volcanic  orifice.  This  might  be  expected  as  the  result  of 

*  "  Rock  "  is  not  used  in  its  geological  or  popular  sense,  but  in  an  old  one,  meaning  a 
distaff. 


VOLCANIC  ACTION  AND   ITS  EFFECTS.  247 

removing  so  much  material  from  beneath  the  crust  and  piling  the 
same  upon  it  over  a  limited  area — not  to  mention  the  effect  which 
would  be  produced  by  the  shrinking  of  the  once  heated  mass  below 
as  it  gradually  cooled.  So  even  such  lofty  volcanic  mountains  as 
Etna  and  Teneriffe,  as  Loa  and  Kea,  in  the  Sandwich  Islands,  are 
wholly  formed  of  the  materials  ejected  from  orifices  which  at  first 
were  but  little  above  the  sea  level,  and  in  some  cases  probably  were 
actually  a  considerable  distance  below  it. 

It  must  not  be  supposed  that  the  whole  of  a  mountain  apparently 
volcanic  is  invariably  constituted  of  ejected  materials.  Orifices  may 
open  on  a  plateau  or  on  some  part  of  mountain  masses  which  are 
already  of  considerable  elevation.  This,  indeed,  is  true  of  many, 
if  not  most,  of  the  highest  volcanoes ;  no  inconsiderable  proportion 
— perhaps  as  much  as  two-fifths,  possibly  more — of  such  summits 
as  Elbruz  and  Kazbek  in  the  Caucasus,  or  of  the  Andes  of  the 
equator,  must  consist  of  rocks,  whether  sedimentary  or  crystalline, 
which  belong  to  an  epoch  long  prior  to  the  volcanic  explosions. 
Still,  every  one  of  the  actual  peaks  about  Quito,  peaks  rising  from 
about  six  thousand  to  eleven  thousand  feet  above  the  upland  mass 
which  may  be  regarded  as  their  common  foundation,  consists,  so  far 
as  known,  of  volcanic  materials. 

Facts  such  as  these  give  some  idea  of  the  enormous  quantity  of 
this  ejected  material.  The  suggestion  has  been  sometimes  made 
that,  as  the  world  is  waxing  old  and  its  energy  is  being  dissipated, 
the  volcanic  phenomena  of  the  present  era  are  feeble  and  puny 
compared  with  the  outbreaks  of  its  hot  and  lusty  youth.  This 
should  be  so,  and,  no  doubt,  in  a  sense  is  so ;  but,  as  Lord  Kelvin 
has  pointed  out,  the  very  fact  that  a  gradual  loss  of  heat  results  in 
a  thickening  of  the  crust  may  cause  the  explosive  phenomena  to  be, 
indeed,  more  unfrequent  and  localized,  but  more  violent  when  they 
do  occur — may  produce,  in  short,  the  effect  of  screwing  down  a 
safety  valve.  So  that  the  masses  of  material  ejected  during  late 
geologic  or  even  historic  times  may  be  quite  comparable  with  those 
which  were  discharged  in  much  earlier  ages,  after  every  allowance 
has  been  made  for  what  may  have  been  removed  by  denudation. 
The  Sandwich  Islands  consist  almost  wholly  of  volcanic  material, 
the  amount  of  coral  reef  or  rock  composed  of  organic  debris  being 
comparatively  trifling.  They  have  been  built  up,  certainly  from 
sea  level,  probably  from  greatly  below  it — for  in  that  part  of  the 
ocean  the  general  depth  of  its  floor  is  at  least  2000  fathoms — 
to  heights  in  some  cases  of  not  less  than  the  same  amount  above 


248  THE   STORY  OF  OUR  PLANET. 

its  surface.  They  are,  in  fact,  as  Professor  Dana  states,  "  a  line  of 
great  volcanic  mountains.  Fifteen  volcanoes  of  the  first  class  have 
existed,  and  have  been  in  brilliant  action  along  the  line.  All  but 
three  are  now  extinct,  and  these  three  are  on  the  easternmost  and 
largest  island  of  the  group — Hawaii.  Hawaii  is  made  out  of  five  of 
the  volcanic  mountains,"  two — Kea,  13,805  feet,  and  Loa,  13,675 
feet — being  much  higher  than  the  rest  (Fig.  98).  Its  area  is  3950 
square  miles,  and  the  whole  area  of  the  group  is  6040  square 
miles.*  Doubtless  this  piling  up  of  mountains  of  scoria  and  lava — 
though  in  all  probability  the  beginning  of  the  island  was,  geologically 
speaking,  a  comparatively  late  event — has  occupied  many  thousands 
of  years.  Still  the  stream  already  mentioned,  which  escaped  from 
the  one  crater  of  Kilauea,  and  had  a  total  course  of  39  miles,  though 
a  mere  driblet  compared  with  the  mass  of  Hawaii,  would  be  regarded 
as  an  important  lava  current  at  any  geological  epoch.  So,  too, 
the  great  basalt  sheets  which  in  Tertiary  ages  welled  up  from 
countless  fissures  in  Idaho,  or  those  which  can  be  traced — though 
now  but  as  fragments — along  the  west  coast  of  Scotland  from 
the  North  of  Skye  even  across  the  sea  to  Antrim,  are  comparable 
with  any  which  have  been  discovered  among  the  older  rocks.  To 
conclude  with  a  single  example,  and  that  barely  more  than  a  cen- 
tury old — Skaptar  Jokull,  in  Iceland.  This  volcano  entered  upon  a 
stage  of  violent  eruption  in  the  summer  of  1783.  Besides  the  usual 
discharges  of  steam,  scoria,  and  similar  materials,  it  emitted  two 
enormous  masses  of  lava.  The  one  was  45  miles,  the  other  50  miles 
long.  They  flowed  in  opposite  directions  along  valleys,  and  rose  up 
in  the  narrower  defiles  to  a  height  of  about  600  feet,  but  attained 
commonly  a  thickness  of  100  feet ;  in  the  more  open  country  they 
broadened  out,  in  the  one  case,  to  about  7,  in  the  other  to  even 
as  much  as  15  miles  across.  Had  the  volcano  arisen  on  the  site 
of  the  city  of  London,  and  the  structure  of  the  country  permitted, 
the  one  stream  would  have  reached  to  beyond  Hassocks,  and  the 
other  almost  to  Cambridge.  Probably  the  quantity  of  lava  ejected 
would  have  sufficed  to  bury  the  whole  county  of  Norfolk  beneath 
a  layer  100  yards  thick. 

It  will  naturally  be  asked,  What  is  the  cause  of  a  volcanic  erup- 
tion ?  The  facts  cited  above  clearly  indicate  that  steam  generally 
issues  from  a  volcano,  and  is  discharged  in  vast  quantities  during  its 

*See  Professor  J.  D.  Dana's  "  Characteristics  of  Volcanoes,"  p.  25,  and  Captain  C.  E. 
Button's  "  Hawaiian  Volcanoes,"  Fourth  Annual  Report  of  the  United  States  Geological 
Survey,  p.  81. 


VOLCANIC  ACTION  AND   ITS  EFFECTS.  24$ 

paroxysmal  phases.  After  the  eruption  of  Etna,  in  1863,  Professor 
Fouque  attempted  to  estimate  the  amount  of  water  which  had  been 
ejected  in  the  form  of  steam,  and  arrived  at  the  conclusion  that 
about  79  cubic  yards  of  water  were  thus  discharged  by  each 
explosion.  As  these  occurred  on  an  average  once  in  four  min- 
utes for  a  hundred  days,  the  total  quantity  of  water  emitted  would 
amount  to  2,829,600  cubic  yards,  enough  to  form  a  lake  about  4000 
yards  long,  700  wide,  and  10  deep.  The  calculation  was  founded 
only  on  the  steam  discharged  from  Monte  Frumento,  an  important 
lateral  cone,  and  the  site  of  the  actual  eruption.  The  central  cone 
also  ejected  considerable  quantities,  of  which,  however,  no  estimate 
was  attempted. 

The  explosive  force  of  steam  is  well  known  to  all ;  boilers  some- 
times give  an  experimental  demonstration,  with  melancholy  results. 
Even  the  British  householder  and  his  careless  servants  occasionally 
receive  an  impressive  object  lesson  when  the  kitchen  boiler  has 
been  allowed  to  run  dry  and  water  has  been  suddenly  let  in 
upon  its  red-hot  plates.  But  a  lava  stream,  as  it  was  flow- 
ing down  the  slopes  of  Etna  in  1843,  once  gave  a  demonstra- 
tion on  a  grander  and  more  disastrous  scale.  "  A  crowd  of  spec- 
tators, who  had  come  from  the  town  (Bronte),  were  examining  at  a 
distance  the  threatening  mass,  the  peasants  were  cutting  down  the 
trees  in  their  fields,  others  were  carrying  off  in  haste  the  goods  from 
their  cottages,  when  suddenly  the  extremity  of  the  flow  was  seen  to 
swell  up,  like  an  enormous  blister,  and  then  to  burst,  darting  forth  in 
every  direction  clouds  of  steam  and  volleys  of  burning  stones. 
Everything  was  destroyed  by  this  terrible  explosion — trees,  houses, 
and  cultivated  ground — and  it  is  said  that  sixty-nine  persons,  who 
were  knocked  down  by  the  concussion,  perished  immediately  or  in 
the  space  of  a  few  hours.  This  disaster  was  occasioned  by  the  neg- 
ligence of  an  agriculturist,  who  had  not  emptied  the  reservoir  on  his 
farm ;  the  water,  being  suddenly  converted  into  steam,  had  caused 
the  lava  to  explode  with  all  the  force  of  gunpowder."  * 

Geysers  also  strongly  support  the  idea  that  steam  is  an  important, 
if  not  the  main,  agent  in  the  characteristic  phenomena  of  a  volcanic 
eruption.  A  geyser,  as  already  said,  may  be  termed  a  water  volcano, 
for  it  ejects  this  instead  of  scoria  and  lava.  It  consists  of  a  cone  or 
mound,  which  usually  rises  a  few  feet  above  the  general  surface  of 
the  ground  ;  in  the  middle  of  this  is  a  crater,  from  the  bottom  of 

*  Reclus,  "  The  Earth,"  ch.  Ixvii. 


25*  THE   STORY  OF  OUR  PLANET. 

which  a  pipe  leads  down  into  the  earth.  Here  also  the  cone  is 
built  up  by  the  geyser  itself  ;  a  certain  amount  of  silica  is  dissolved 
in  the  boiling  water,  and  as  the  later  rapidly  cools  when  it  falls  in 
showers  round  about  the  orifice,  the  mineral  is  precipitated.  Com- 
monly the  basin  of  the  geyser  is  full  of  clear  water,  and  a  little 
steam  curls  up  quickly  from  its  surface,  but  now  and  again  an  erup- 
tion takes  place,  sometimes  at  intervals  singularly  regular — as  in 
the  case  of  Old  Faithful  at  the  Yellowstone  Park — but,  as  with  the 
Great  Geyser  of  Iceland,  more  often  at  irregular  intervals.  Occa- 
sionally, indeed,  artificial  means  can  be  employed  to  produce  an 
eruption ;  this  is  the  case  with  one  of  the  smaller  geysers  in  the 
Icelandic  region,  which  is  called  Strokr,  or  the  Churn.  A  barrow 
load  of  sods  is  thrown  into  the  throat  of  the  geyser ;  this  not  un- 
naturally turns  its  stomach,  and  has  all  the  effect  of  an  emetic. 
The  sensitiveness  of  Strokr  is  due  to  its  peculiar  form.  "  The  bore 
is  8  feet  in  diameter  at  the  top,  and  44  feet  deep.  Below  27  feet  it 
contracts  to  19  inches,  so  that  the  turf  thrown  in  completely  chokes 
it.  Steam  then  generates  ;  a  foaming  scum  covers  the  surface  of 
the  water,  and  in  a  quarter  of  an  hour  it  surges  up  the  pipe,  allow- 
ing one  ample  time  for  escape  to  the  edge  of  the  saucer.  The  fountain 
then  begins  playing,  sending  its  bundles  of  jets  rather  higher  than 
those  of  the  Great  Geyser,  flinging  up  the  clods  of  turf,  which  have 
been  its  obstruction,  like  a  number  of  rockets.  This  magnificent  dis- 
play .continues  for  a  quartef  of  an  hour  or  twenty  minutes.  The 
erupted  water  flows  back  into  the  pipe  from  the  curved  sides  of  the 
bowl.  This  occasions  a  succession  of  bursts,  the  last  expiring  effort, 
very  generally,  being  the  most  magnificent.  Strokr  gives  no  warning 
thumps,  like  the  Great  Geyser,  and  there  is  not  the  same  roaring 
of  steam  accompanying  the  outbreak  of  the  water."  The  same 
author  *  thus  describes  an  eruption  of  the  Great  Geyser,  which 
occurred  about  two  o'clock  in  the  morning:  "  A  violent  concussion 
of  the  ground  brought  me  and  my  companions  to  our  feet.  We 
rushed  out  of  the  tent  in  every  condition  of  deshabille  and  were  in 
time  to  see  Geyser  put  forth  his  full  strength.  Five  strokes  under- 
ground were  the  signal,  then  an  overflow,  wetting  every  side  of  the 
mound.  Presently  a  dome  of  water  rose  in  the  center  of  the  basin 
and  fell  again,  immediately  to  be  followed  by  a  fresh  bell,  which 
sprang  into  the  air  full  40  feet  high,  accompanied  by  a  roaring  burst 
of  steam.  Instantly  the  fountain  began  to  play  with  the  utmost 

*S.   Baring-Gould,  "  Iceland :  Its  Scenes  and  Sagas,"    ch.  xxi. 


VOLCANIC  ACTION  AND  ITS  EFFECTS.  251 

violence,  a  column  rushed  up  to  the  height  of  90  or  100  feet  against 
the  gray  night  sky,  with  mighty  volumes  of  white  steam  cloud  roll- 
ing about  it,  and  swept  off  by  the  breeze  to  fall  in  torrents  of  hot 
rain.  Jets  and  lines  of  water  tore  their  way  through  the  clouds,  or 
leaped  high  above  its  domed  mass.  The  earth  trembled  and 


FIG.  107.— SECTION  OF  THE  GREAT  GEYSER. 


throbbed  during  the  explosion;  then  the  column  sank,  started  up 
again,  dropped  once  more,  and  seemed  to  be  sucked  back  into  the 
earth.  We  ran  to  the  basin,  which  was  left  dry,  and  looked  down 
the  bore  at  the  water,  which  was  bubbling  at  the  depth  of  6  feet." 
In  the  case  of  Strokr  the  cause  of  the  eruption  seems  obvious; 
the  turf  chokes  up  the  narrow  part  of  the  pipe,  the  steam  is  pre- 
vented from  escaping,  until  at  last  it  removes  the  obstacle  with 
explosive  violence,  just  as  a  bottle  of  fermenting  liquor,  imperfectly 
secured,  may  blow  out  the  cork  and  discharge  some  of  its  contents. 


252  THE   STORY  OF  OUR  PLACET. 

In  the  case  of  the  Great  Geyser,  while  it  is  pretty  evident  that 
steam  has  much  to  do  with  the  eruption,  the  exact  cause  is  not  so 
clear,  and  several  explanations  have  been  proposed.  But  there  can 
be  little  doubt  that  the  right  one  has  at  last  been  found.  Certain 
facts  have  been  ascertained,  as  the  Great  Geyser  has  been  carefully 
studied  by  successive  observers,  of  which  account  must  be  taken  in 
attempting  any  explanation.  The  shaft  is  about  75  feet  in  depth. 
Its  diameter,  which  is  about  10  feet,  continues  uniform  to  the  bottom, 
but  a  sort  of  ledge  exists  on  one  side,  at  a  depth  of  about  44  feet, 
which  is  called  after  its  discoverer,  Bunsen,  the  eminent  philosopher. 
From  beneath  this  ledge,  when  the  tube  has  been  emptied  by  an 
exceptionally  violent  series  of  explosions,  steam  has  been  observed 
to  escape,  so  that  it  must  signify  the  mouth  of  a  lateral  orifice. 
This  roughly  indicates  the  lower  limit  of  the  explosive  phenomena, 
for  if  stones  attached  to  strings  of  various  lengths  are  suspended  in 
the  shaft,  those  above  this  ledge  are  ejected  during  the  eruption, 
while  those  which  hang  down  below  it  are  not  disturbed.  The  tem- 
perature of  the  water  in  the  shaft  has  also  been  observed  at  differ- 
ent depths.  Pressure,  it  must  be  remembered,  affects  the  boiling 
point  of  water,  so  that  even  if  ebullition  took  place  on  the  surface 
of  the  basin,  this  would  not  be  the  case  in  the  shaft  unless  the  water 
was  raised  to  a  higher  temperature,  the  amount  of  which  would 
depend  on  the  depth.  At  the  bottom  of  the  shaft  the  water  would 
not  boil  till  it  was  raised  to  a  temperature  of  nearly  257°  instead  of 
212°  F.  The  temperature  at  the  top  of  the  shaft  is  186°  F. ;  it  is 
found  to  increase  in  proportion  to  the  depth  from  the  surface,  but 
it  nowhere  attains  the  boiling  point  for  the  depth.  Just  on  the 
level  of  the  ledge  the  difference  between  the  actual  temperature 
and  that  required  for  boiling  is  slightly  less  than  4°  F.  If,  then,  by 
any  means  the  layer  of  water  at  this  level  can  be  suddenly  lifted  up 
only  six  feet,  it  will  have  reached  a  horizon  where  the  boiling  tem- 
perature is  rather  more  than  a  degree  below  its  own  temperature. 
A  sudden  and  explosive  development  of  steam  will  be  the  result, 
which  will  raise  the  contents  of  the  upper  part  of  the  pipe  and  dis- 
charge some  of  them  into  the  air.  More  water  is  then  brought  to  a 
level  where  it  can  flash  into  steam,  and  the  discharge  has  helped  in 
diminishing  pressure,  so  that  explosions  yet  more  violent  occur. 
Like  the  shot  in  a  gun  when  the  powder  is  ignited,  the  whole 
"  charge  "  of  water  is  shot  up  from  this  huge  blunderbuss,  but  it 
drops  back  quickly  into  the  barrel  ;  steam  is  thus  imprisoned  ;  there 
is  a  recoil  as  of  a  spring,  and  a  new  discharge.  So  the  geyser  plays 


VOLCANIC  ACTION  AND  ITS  EFFECTS.  253 

till  the  steam  has  managed  to  escape  and  much  of  the  water  has 
been  spilt.  Observers  of  a  geyser  in  eruption  have  frequently 
recorded  that  a  loud  rush  of  steam  is  the  signal  that  the  display  is 
at  an  end. 

The  geysers  doubtless  exhibit  local  variations,  but  the  story  of 
this  one  seems  to  leave  no  room  for  doubt,  and  the  interpretation 
proposed  to  explain  the  facts  has  been  verified  by  experiment ;  for 
Professor  Tyndall  constructed  in  his  laboratory  at  the  Royal  Insti- 
tute a  working  model  of  the  Great  Geyser,  and  produced  an  erup- 
tion by  rilling  with  hot  embers  a  small  chafing  dish  constructed 
round  the  middle  part  of  the  tube.*  We  seem,  then,  justified  in 
adopting  this  conclusion — that  as  an  eruption  of  water  in  the  case 
of  the  Great  Geyser  is  produced  by  an  accumulation  of  steam,  which 
leads  to  a  further  explosive  development  of  vapor,  so  in  regard  to 
ordinary  volcanoes,  whatever  kind  of  materials  may  be  ejected,  the 
actual  eruption,  the  explosive  phenomena,  are  due  to  the  action  of 
steam.  Gases  of  various  kinds  may  contribute  to  the  general  result, 
but  there  can  be  no  doubt  that  the  vapor  of  water  plays  the  largest 
part. 

The  geographical  relations  of  volcanoes  are  also  significant. 
Some,  it  is  true,  at  first  sight  appear  disconnected  in  position  and 
sporadic  in  distribution,  but  even  these  in  many  cases  prove,  on 
closer  study,  to  be  merely  the  survivors  of  a  much  more  numerous 
band  of  volcanoes,  for  they  are  linked  together  by  ruined  cones. 
Thus  Etna,  Vesuvius,  and  the  Lipari  Islands  are  the  last  remains  of 
a  much  more  extensive  series  of  Italian  volcanoes.  Those  of  the 
Greek  Archipelago  seem  to  form  a  separate  Mediterranean  group. 
In  the  Atlantic  the  number  of  active  volcanoes  is  small,  but  Iceland 
marks  the  last  cluster  of  open  vents  on  a  long  but  interrupted  line, 
of  which  one  end  may  be  placed  on  the  west  coast  of  Greenland, 
the  other  in  Antrim,  whither  it  can  be  traced  through  the  Faroe 
Islands  and  along  the  western  coast  of  Scotland.  The  Azores, 
Canaries,  and  Cape  de  Verde  Islands  mark  the  position  of  another 
series  of  craters,  now  almost  extinct,  which  may  be  traced  south- 
ward by  St.  Helena  and  Tristan  d'Acunha.  Rodriguez,  Mauritius, 
and  Bourbon  on  the  eastern  side  of  Africa  indicate  another  volcanic 
chain  somewhat  similar  in  situation  ;  and  on  the  mainland,  east  and 
west,  volcanoes  which  have  now  become  extinct  and  sometimes  are 
in  ruins,  such  as  the  Camaroons  or  Kilimanjaro,  occasionally  occur. 

*The  model  is  described  in  his  book  entitled  "  Heat,  a  Mode  of  Motion,"  ch.  iv. 


254  THE   STORY  OF  OUR  PLANET. 

Not  till  the  eastern  side  of  the  Indian  Ocean  and  the  Pacific  is 
approached  do  volcanic  mountains  become  comparatively  common 
or  is  their  connection  strongly  marked.  With  the  Andaman  Islands, 
in  the  Bay  of  Bengal,  begins  a  linear  series  of  volcanoes  which 
passes  through  Sumatra,  Java,  and  the  smaller  islands  east  of  the 
latter  to  the  western  end  of  New  Guinea.  Here  a  great  spur  is 
thrown  off  to  the  north  as  the  volcanic  belt  continues  on  through 
that  island  and  sweeps  by  the  Solomon  and  other  small  islands  to 
New  Zealand.  The  spur  just  mentioned  takes  a  northwestward 
course  to  the  Philippine  Islands,  but  the  volcanoes  in  Borneo  on 
the  one  hand,  and  the  Marianne  Islands  on  the  other,  indicate 
that  in  this  region  a  very  large  area  of  the  earth's  crust  is  subject 
to  these  disturbances.  From  the  north  end  of  the  Philippines 
a  linear  arrangement  of  the  vents  again  becomes  more  or  less 
conspicuous.  They  run  almost  parallel  with  the  China  coast  to 
Japan,  and  are  continued  through  the  Kurile  Islands  to  the  long 
peninsula  of  Kamtschatka,  on  which  they  are  studded.  The  end  of 
the  continent  of  Asia  only  slightly  interrupts  the  continuity  of  this 
chain  of  furnaces ;  it  begins  again  in  the  Aleutian  Islands,  reaches 
the  American  mainland,  and  runs  on  through  Alaska.  In  the 
northern  part  of  the  American  continent  active  volcanoes  become 
for  a  time  few  and  far  between,  but  at  no  distant  epoch,  geologically 
speaking,  they  were  scattered  along  the  mountains  on  the  western 
border  of  the  continent,  almost  from  one  end  to  the  other.  Among 
these  extinct  craters  or  ruined  cones  are  frequent.  The  ranges  in 
the  west  of  British  Columbia,  the  chain  of  the  Cascades  in  Oregon, 
the  parallel  ranges  of  the  Sierre  Nevada,  and  the  Rocky  Mountains 
are  dominated  by  volcanoes ;  but  only  a  few  of  these  continue  to 
eject  occasionally  steam  and  ash,  such  as  Mount  Fairweather  in  the 
extreme  north,  and  Mount  Edgecumbe  on  Lazarus  Island,  or  Mount 
Baker,  Mount  Renier,  and  Mount  St.  Helen's  in  the  United  States 
territory.  Indications  of  eruptions  comparatively  recent  may  be 
traced  through  California  and  Northern  Mexico,  while  Central 
Mexico  is  a  region  of  active  volcanoes,  ma  ly  of  which  are  of  a  gigantic 
size.  Hence  the  line  of  vents  continues  along  the  rapidly  narrowing 
continent ;  the  low  isthmus  of  Panama  is  cnly  a  temporary  interrup- 
tion, and  they  break  out  with  renewed  fury  in  South  America. 
The  Andes,  from  one  end  of  the  chain  to  the  other,  culminate  in 
volcanic  cones,  which  are  still  fairly  active  in  three  distinct  regions — • 
namely,  in  Ecuador,  Peru,  and  Chili.  It  is  doubtful,  indeed,  whether 
this  line  of  disturbance  is  not  prolonged  far  to  the  south  of  the 


VOLCANIC  ACTION  AND  ITS  EFFECTS.  255 

American  continent,  for,  nearly  opposite  to  Cape  Horn,  Mounts 
Erebus  and  Terror  rise  like  twin  beacons  near  the  margin  of  the 
Antarctic  land.  An  offshoot  from  this  enormous  belt  of  fire  may 
be  traced  in  South  America  along  the  south  shore  of  the  Caribbean 
Sea  to  the  Antilles,  while  in  an  opposite  direction  the  sporadic 
groups  of  the  Galapagos,  Society,  and  Tonga  islands  may  indicate 
the  existence  of  a  zone  which  bridges  the  Pacific  and  links  together 
the  two  great  belts  which  border  its  eastern  and  western  shores. 
The  Sandwich  Islands  volca-noes  also  assume  a  somewhat  linear 
order,  though  there  are  difficulties  in  joining  these  on  to  any  of  the 
other  series. 

All  these  volcanoes,  it  will  be  observed,  rise  either  directly  from 
the  ocean  or  within  a  moderate  distance  of  its  coasts.  Nor  is  this 
all,  for  if  a  search  be  made  for  volcanoes  in  the  interior  of  con- 
tinents, it  almost  always  proves  fruitless.  One  or  two  vents  still 
active  are  said  to  exist  in  Mongolia,  but  the  fact  is  far  from  being 
well  established.  Demavend,  at  first  sight,  appears  to  be  an  excep- 
tion, but  even  it  is  situated  on  the  shores  of  the  Caspian.  Such  a 
survey  as  that  which  has  been  briefly  indicated  appears  to  lead  to 
two  inferences — one,  that  volcanoes  are  commonly  arranged  in  lines; 
the  other,  that  when  active  they  are  generally  in  the  neighborhood 
of  large  sheets  of  water.*  The  former  fact  suggests  a  connection 
between  volcanic  vents  and  lines  of  weakness  or  fracture  in  the 
earth's  crust ;  the  latter  that  their  paroxysmal  activity,  perhaps 
even  their  existence,  depends  upon  the  proximity  of  water,  so  that 
"  without  water  no  eruption "  might  almost  be  regarded  as  an 
axiom.  A  corroboration  of  this  relation  is  found  in  the  fact  that 
common  salt  is  among  the  products  of  an  eruption.  In  Sicily  the 
slopes  of  Etna  are  sometimes  white  with  a  saline  efflorescence,  and 
in  Iceland  the  salt  which  remains  behind  on  Hecla,  after  the  fallen 
water  has  evaporated,  is  said  to  be  occasionally  in  sufficient  abun- 
dance to  be  collected  by  the  peasants.  Moreover,  it  has  been 
observed  that  almost  all  the  constituents  of  sea-water  occur  in  erup- 
tive products,  the  bromine  salts  alone  not  yet  having  been  detected. 
Diatoms  also,  both  fresh-water  and  marine,  have  been  found  in  vol- 
canic ashes,  and  those  discovered  by  Ehrenberg,  near  the  Laacher 
See,  are  said  to  have  been  partially  fused.  To  whatever  cause, 
then,  the  occurrence  of  great  masses  of  molten  rock  may  be  attrib- 
uted— which  must  be  presently  considered — the  evidence  seems 

*  Great  lakes  existed  in  Auvergne  at  the  time  of  the  more  important  volcanic  eruptions. 


256  THE   STORY  OF  OUR  PLANET. 

strong  in  favor  of  regarding  eruptive  phenomena  as  very  largely 
due  to  the  effects  of  water.  But  if  the  explosions  may  be  attrib- 
uted to  the  conversion  of  water  into  steam,  either  by  contact  with 
heated  rock  or  by  the  sudden  removal  of  pressure  which  retained  it 
in  a  liquid  condition  in  a  molten  mass,  if  the  outward  flow  of  the 
lava  is  due  to  similar  but  less  paroxysmal  action,  by  what  cause  or 
causes  has  this  mass  been  melted?  It  is  believed  with  good  reason, 
as  will  be  presently  seen,  that  the  temperature  of  the  earth's  interior 
is  very  high.  From  a  short  distance -below  the  actual  surface  there 
is  a  gradual  increase  of  heat  in  descending,  so  that  a  temperature  of 
2000°  F.  is  probably  reached  at  a  depth  of  about  twenty-two  or 
twenty-three  miles.  This,  as  already  said,  is  about  the  melting 
point  of  several  kinds  of  rock,  so  that  if  by  any  means  a  mass  could 
be  forced  up  to  the  surface  from  such  a  depth  without  materially 
cooling,  it  would  become  liquid,  even  though  it  had  previously 
remained,  owing  to  the  great  pressure,  in  a  solid  condition.  The 
above-named  depth,  however,  may  be  regarded  as  a  minimum,  and 
it  would  often  be  necessary  to  bring  up  the  materials  from  at  least 
twenty-five  or  sometimes  full  thirty  miles  ?  so  that  difficulties  have 
been  felt  as  to  the  existence  of  a  motive  force  which  would  be  com- 
petent to  raise  materials  quickly  from  so  great  a  distance  beneath 
the  surface.  In  the  hope  of  avoiding  these,  various  hypotheses 
have  been  advanced  to  account  for  a  development  of  heat  at  more 
moderate  depths  which  would  be  sufficient  to  melt  rocks  already 
solid. 

The  late  Sir  Humphry  Davy  suggested  that  heat  was  developed 
by  chemical  action  in  the  following  way :  He  assumed  that  the 
earth's  interior,  within  a  comparatively  short  distance  from  the  sur- 
face, consisted  of  metallic  substances  not  yet  combined  with  oxygen. 
He  supposed  that  as  water  percolated  downward  it  came  into  con- 
tact with  this  inner  mass,  and  its  oxygen  entered  into  new  combina- 
tions,* thus  producing  an  amount  of  heat  sufficiently  great  to  melt 
the  neighboring  rocks.  But  he  ultimately  abandoned  the  hypoth- 
esis on  the  ground  that  the  "  flames "  of  a  volcano,  instead  of 
being  burning  hydrogen  gas,  were  only  the  glow  of  the  molten  rock 
reflected  on  the  steam.  Of  late  years  the  force  of  this  objection 
has  been  weakened,  for  the  flame  of  burning  hydrogen  has  been  not 
seldom  observed  in  a  volcanic  eruption.  The  quantity,  however,  is 
not  sufficient,  really,  to  overcome  the  difficulty,  and  another  one 

*  Oxygen  also  would  be  present  in  solution  in  the  water. 


VOLCANIC  ACTION  AND  ITS  EFFECTS.  257 

has  been  brought  forward,  which  is  even  more  serious — viz.,  the 
magnitude  of  the  mass  which  must  be  oxidized  in  a  comparatively 
short  time  in  order  to  develop  a  sufficient  amount  of  heat.  For 
instance,  it  was  calculated  by  Professor  Fouque  that  the  amount  of 
heat  disengaged  in  the  eruption  of  Etna — which,  as  already  men- 
tioned, he  carefully  studied — would  require  a  mass  of  sodium  to 
have  been  oxidized  which  measured  one  hundred  meters  in  length 
and  breadth  and  seven  hundred  meters  in  height. 

Some  authors  have  considered  the  heat  to  be  produced  by  mag- 
netic currents.  Such  undoubtedly  exist,  but  so  little  is  known  at 
present  of  either  these  or  their  effects  that  any  appeal  to  them  in 
explanation  of  a  difficulty  is  like  expounding  a  parable  by  a  riddle, 
and  it  may  be  doubted  whether  either  these  currents  or  the  local 
resistances  to  them  are  sufficiently  strong  to  develop  enough  heat 
to  raise  the  temperature  of  a  large  mass  of  rock  by  some  hundreds 
of  degrees. 

Another  solution  of  the  difficulty  was  propounded  by  the  late 
Mr.  Mallet,  which,  however  ingenious  it  may  be  as  an  exercise  in 
mathematical  physics,  obtains  very  little  support  from  any  known 
geological  facts.  Assuming  the  earth  to  have  been  once  a  molten 
mass,  and  to  lose  heat  by  radiation,  it  would  be  covered,  after  a 
time,  with  a  thick  crust.  As  the  inner  part  continued  to  cool,  and 
so  to  contract,  it  would  tend  to  shrink  away  from  the  crust ;  this 
accordingly  would  cease  to  be  strained,  and  be  subjected  to  thrusts. 
The  amount  of  these  can  be  estimated,  and  Mr.  Mallet  came  to  the 
conclusion  that  the  pressures  thus  developed  would  be  more  than 
sufficient  to  crush  to  powder  any  of  the  rocks  which  enter  into  the 
composition  of  the  earth's  crust.  As  the  latter  is  not  of  uniform 
strength  throughout,  it  would  yield  locally,  and  the  crushing  would 
be  sudden  and  restricted  to  comparatively  limited  areas.  But  when 
rock  is  thus  crushed,  heat  is  developed.  The  amount  of  this  also 
can  be  calculated.  According  to  Mr.  Mallet,  the  heat  yrhich  would 
result  from  crushing  I  cubic  foot  of  ordinary  rock  would  suffice  to 
raise  3^  cubic  feet  of  the  same  to  a  temperature  of  2000°  F. — or, 
in  other  words,  to  melt  it.  Thus,  in  his  view,  a  certain  portion  of 
the  heat  given  off  by  radiation  is  utilized  in  doing  work  in  the 
outer  crust  of  the  earth,  and  is  there  locally  reconverted.  So  far  as 
he  could  estimate,  the  transformation  into  heat  of  the  energy 
expended  in  crushing  about  247  cubic  miles  of  average  rock,  or 
one-quarter  of  the  heat  which  the  globe  annually  loses  by  radia- 
tion, would  suffice  to  account  for  all  its  volcanic  phenomena. 


258  THE   STORY  OF  OUR  PLANET. 

But  this  explanation,  promising  as  it  may  seem,  is  attended  with 
most  serious  difficulties.  For  instance,  in  many  cases  no  connec- 
tion can  be  established  between  a  volcanic  region  and  one  where 
earth  movements  on  an  important  scale  are  in  process.  The  vents, 
indeed,  may  mark  the  position  of  a  line  of  fracture  or  weakness,  but 
this  is  likely  to  indicate  strain  rather  than  compression.  It  is  also 
very  doubtful  whether,  even  in  the  latter  case,  the  rock  would  be 
suddenly  crushed  in  masses  sufficiently  large  to  produce  any  very 
material  elevation  of  temperature.  The  destructive  process  in  all 
probability  would  be,  comparatively  speaking,  a  gradual  one,  and 
the  heat  thus  generated  would  be  dissipated  without  producing  any 
very  marked  effect.  But  in  this  respect  it  is  possible  to  submit  the 
hypothesis  to  a  kind  of  test.  It  is  generally  admitted  by  geologists 
that  many  rock  masses,  both  sedimentary  and  crystalline,  have  been 
subjected  to  great  compression,  by  which  they  have  been  folded  or 
cleaved,  or  sometimes  actually  crushed.  Here,  then,  in  such  a 
region  as  the  Alps,  where  it  can  be  proved  often  that  a  granite  has 
been  converted  by  crushing  into  a  kind  of  schist,  where  the  whole 
process  of  mechanical  change  can  be  traced  in  every  stage,  some 
indications  should  be  found  of  such  a  result  as  Mr.  Mallet's  hypoth- 
esis requires.  The  minutest  structure  of  the  rock  in  each  phase 
can  be  studied  under  the  microscope — if  a  bit  had  been  melted,  this 
could  be  recognized  almost  at  a  glance,  even  were  it  no  larger  than 
a  small  pin's  head.  But  what  is  the  result  ?  The  heat  generated 
may  have  been  sufficient  to  facilitate  chemical  change — for  evi- 
dently, as  an  indirect  result  of  the  crushing,  numerous  minerals 
have  been  developed,  which,  however,  generally  are  of  very  small 
size — but  of  any  melting,  in  the  proper  sense  of  the  word,  of  any 
conversion  of  the  rock  either  into  a  volcanic  glass  or  into  a  crystal- 
line mass  which  may  be  produced  under  certain  circumstances  from 
the  material  of  such  a  glass,  not  the  slightest  trace  can  be  found. 
So  that  this  hypothesis,  attractive  as  it  may  be  at  first  sight,  appears 
to  be  destitute  of  any  real  foundation. 

Difficult,  then,  as  it  may  be  to  understand  the  precise  agency  by 
which  masses  of  rock  can  be  forced  up  to  the  neighborhood  of  the 
surface  from  depths  of  twenty  to  thirty  miles,  we  fail  to  find  any 
explanation  of  the  high  temperature,  which  is  evidently  a  primary 
condition  of  volcanic  action,  more  satisfactory  than  the  proper 
internal  heat  of  the  earth.  This,  on  the  whole,  is  more  accordant 
than  any  other  with  the  present  distribution  of  volcanoes  ;  it  is 
most  in  harmony  with  the  phenomena,  not  only  pf  volcanoes  still 


VOLCANIC  ACTION  AND  ITS  EFFECTS.  259 

active,  but  also  of  igneous  rocks  in  general.  The  chief  volcanic 
regions  of  the  globe,  as  already  observed,  either  traverse  or  fringe 
the  greater  ocean  basins.  As  will  be  seen  later  on,  when  the  evolu- 
tion of  land  masses  is  discussed,  the  principal  regions  for  the  deposit 
of  sediment,  and  ultimately  for  processes  of  upheaval,  folding,  and 
mountain  making,  are  those  parts  of  the  ocean  basin  which  border 
the  continents.  Here,  it  must  be  remembered,  the  water  is  com- 
paratively shallow ;  the  surface  of  these  masses  of  sediment,  while 
still  submerged,  is  often  some  two  miles  vertically  above  the  gen- 
eral level  of  the  old  floor  over  a  large  part  of  the  ocean.  If,  then, 
the  crust  of  the  earth  is  contracting  from  general  loss  of  heat,  this 
irregularity  in  the  form  of  its  outer  surface,  this  departure  from  a 
true  spherical  outline,  must  tend  to  a  further  distortion  of  form. 
The  inner,  deeper,  and  comparatively  level  part  of  the  trough  may 
move  with  fair  uniformity  as  a  whole,  but  in  so  doing  it  will  act  like 
an  arch  on  its  abutments,  and  produce  thrusts  in  an  upward  and 
outward  direction,  the  effects  of  which  will  be  most  marked  near  its 
margin,  and  will  be  exbibited  by  uplifts  and  folds  in  that  region. 
It  is  therefore  possible  that,  as  a  consequence  of  these  movements, 
masses  of  rock  which  were  still  in  a  plastic  condition  might  be 
gradually  extruded  from  beneath  the  subsiding  margin  of  the 
deeper  ocean  floor  toward  the  rising  zone,  and  might  ultimately  be 
squeezed  into  cracks  and  cavities  among  the  folding  rocks.  Some- 
times these  intruded  masses  may  never  reach  the  surface ;  at  others, 
especially  if  brought  into  contact  with  water,  they  may  break  forth, 
more  or  less  explosively,  as  volcanoes. 

The  -mode  in  which  igneous  rocks  occur  accords  generally  with 
this  idea  of  their  origin.  They  appear  sometimes  to  have  made 
their  way  to  the  surface  along  innumerable  fissures,  as  if  a  large  area 
of  rock  had  been  strained  until  it  yielded,  and  formed  a  series  of 
parallel  gaping  cracks,  through  which  the  molten  matter  flowed ; 
as  may  be  seen  in  the  cliffs  of  the  promontory  of  Strathaird,  in 
Skye  (Fig.  62).  Sometimes  they  have  forced  their  way  under- 
ground between  two  masses  of  uniformly  stratified  rock,  occasionally 
with  singular  regularity,  like  a  paper  knife  thrust  between  the  pages 
of  a  book,  as  if  the  upper  bed  had  been  too  solid  to  allow  further 
progress  in  that  direction,  and  yet  the  pressure  from  below  on  the 
plastic  mass  had  enabled  it  to  rend  the  layers  apart,  and  to  lift  up 
the  overlying  one.  In  a  fashion  somewhat  similar  the  melted 
material  has  occasionally  poured  out  laterally  for  a  more  limited 
space  around  the  upward  channels  of  discharge,  lifting  the  resisting 


260  THE    STORY  OF  OUR  PLANET. 

masses  of  sedimentary  rock  in  the  form  of  a  flattened  dome,  some- 
times even  piercing  into  them  for  a  little  way  by  veins  and  similar 
offshoots,  but  assuming  in  the  main  a  form  rudely  resembling  a 
mushroom.*  That  masses  such  as  these  stand  in  the  closest  possi- 
ble relation  to  the  products  of  active  volcanoes  is  demonstrated  by 
comparison  of  the  one  with  the  other ;  the  lava  streams  and  dykes 
of  the  latter  very  closely  resemble,  if  they  are  not  identical  with, 
the  "  sills  "  and  dykes  of  the  former.  Among  such  rocks,  if  a  series 
of  examples  be  examined  which  are  identical  in  chemical  composi- 
tion, it  is  possible  to  trace  every  stage  of  change,  from  the  compara- 
tively glassy  materiar  which  has  obviously  solidified  at  or  near  the 
surface  of  an  extinct  volcano  to  the  coarsely  crystalline  rock  which 
had  been  cooled  deep  in  the  earth,  and  represents  the  once  hidden 
sources  from  which  formerly  the  lava  streams  were  supplied.  The 
adjacent  rocks  indicate  by  their  condition  that  the  temperature  of 
the  intrusive  mass  was  once  extremely  high.  A  series  of  mineral 
changes  have  been  produced  which  exhibit  every  stage,  from  simple 
induration  or  "  baking,"  in  the  vicinity  of  small  masses,  which 
appear  to  have  rapidly  cooled,  to  the  more  or  less  complete  oblitera- 
tion of  original  structures  and  the  rearrangement  of  constituents  to 
form  new  combinations  in  the  case  of  the  larger  and  deeper  seated 
intruders. 

The  probability  that  igneous  rocks  are  not  produced  by  the  local 
melting  down  of  sediments  increases  when  their  mineral  composi- 
tion and  distribution,  both  in  time  and  space,  are  more  closely 
studied.  If  they  were  thus  connected,  a  fairly  close  correspon- 
dence in  chemical  composition  should  exist  between  the  igneous 
and  the  sedimentary  rocks.  Such  a  correspondence  is  excep- 
tional. Instances,  no  doubt,  of  felspathic  sandstones  or  of 
sandy  shales  can  be  selected  which,  on  analysis,  agree  chemically 
with  granite,  for  the  simple  reason  that  the  breaking  up  of  the  latter 
has  produced  the  former  ;  but  it  is  very  difficult  indeed  to  find 
among  the  sediments  parallels  with  that  very  large  group  of  igneous 
rocks  of  which  basalt  may  be  taken  as  a  type,  while  the  limestones, 
which  are  common  in  the  former,  and  the  olivine  rocks,  which  are 
not  very  rare  among  the  latter,  remain  in  each  case  unmatched.f 
Inferences  as  to  a  common  origin  of  two  classes  of  rock  cannot  be 

*  These  masses  are  technically  called  laccolites. 

f  Although  peridotites  (or  rocks  composed  mainly  of  the  mineral  olivine,  with  little  or 
no  felspar)  are  rare,  still  serpentines  (which  have  been  proved  to  be  merely  altered  perido- 
tites) are  not  very  uncommon. 


VOLCANIC  ACTION  AND  ITS  EFFECTS.  261 

made  by  selecting  exceptional  instances  from  either  side  ;  they 
must  be  founded  on  a  comparison  of  the  ordinary  and  dominant 
types  in  both.  When  this  is  done,  the  sedimentary  rocks  will  be 
found  to  be  generally  either  poorer  in  alkalies  or  richer  in  lime  than 
the  igneous  rocks,  which  in  other  respects  approach  them  most 
nearly  in  chemical  composition,  while  they  fail  to  afford  any 
examples,  like  the  latter  group,  of  rocks  rich  in  ferro-magnesian 
silicates.  Igneous  rocks,  moreover,  appear  to  be  unaffected  either 
by  geographical  position  or  by  geological  age.*  A  basalt  from 
Europe  may  be  indistinguishable  from  one  found  in  Australia.  A 
basalt  which  was  ejected  during  the  ages  when  the  coal  beds  of 
Britain  were  being  formed  may  be  practically  identical  with  one 
collected  from  a  lava  stream  of  recent  date.  All  these  considera- 
tions lead  to  the  conclusion  that,  as  a  general  rule,  the  igneous 
rocks  are  not  portions  of  sedimentary  rocks  locally  melted  down, 
but  represent  the  outer  part  of  the  magma  of  which  the  globe  is 
composed. 

*  For  many  years  the  propriety  of  classifying  igneous  rocks  by  their  geological  age  was 
stoutly  maintained  by  many  geologists,  especially  in  Germany.  In  England  it  found  little 
or  no  support,  and  quite  lately  the  only  argument  in  its  favor  which  had  any  real  value  has 
been  most  seriously  impaired.  This  classification  was  mainly  founded  on  distinctions 
which  were  chiefly  due  to  secondary  changes  ;  they  were  signs  of  difference  in  age,  but  not 
of  difference  in  kind — that  is  to  say,  they  were  hardly  more  valuable  for  purposes  of  classi- 
fication than  the  presence  or  the  absence  of  gray  hairs  on  men. 


CHAPTER   III. 

EARTHQUAKES  AND   THEIR   EFFECTS. 

AN  earthquake  is  caused  by  the  transit  of  a  wave-like  movement 
through  the  crust  of  the  globe.  It  is  a  shudder  of  the  cuticle, 
resulting  from  some  sudden  internal  change  or  catastrophe.  The 
tremor  may  be  so  slight  as  to  be  detected  only  by  the  most  delicate 
instruments  constructed  expressly  to  record  the  faintest  telluric  dis- 
turbance, or  it  may  shatter  the  strongest  buildings,  convert  a  city 
into  a  heap  of  ruins,  and  rend  the  solid  ground.  The  feebler 
shocks  may  be  compared  to  the  vibrations  produced  in  a  slightly 
built  house  by  the  passage  of  a  heavy  train  close  at  hand,  either 
above  ground  or  through  a  tunnel  below  (Londoners  will  appreciate 
the  comparison),  or  to  the  concussion  transmitted,  often  from  con- 
siderable distances,  by  the  explosion  of  a  large  quantity  of  powder. 
The  greater  shocks  are  the  most  terrible  phenomena  in  nature. 
Familiarity  with  them  does  not  breed  contempt,  but  increases  the 
dread  which  they  cause,  for  when  the  solid  earth  rocks  nothing 
seems  secure ;  the  nervous  system  is  shaken  by  the  strangeness  of 
the  experience,  and  above  all  by  the  seeming  treacherousness  of  the 
visitations,  for  the  hurricane  gives  some  warning,  brief  though  it 
may  be,  of  its  approach,  the  volcano  some  indication  that  danger  is 
impending,  but  with  the  earthquake  at  one  minute  all  is  peaceful, 
at  the  next  the  land  is  quivering  like  an  aspen,  prosperity  has  given 
place  to  ruin,  and  joy  to  sorrow. 

Sometimes  only  a  single  shock  is  observed.  This  may  be  almost 
instantaneous  in  its  passage,  or  it  may  consist  of  a  group  of  con- 
tinuous vibrations  of  variable  intensity,  which  may  occupy  some 
minutes — wave  following  wave  along  the  crust,  which  is  occasionally 
seen  actually  to  rise  and  fall  like  the  surface  of  a  liquid.  Some- 
times .also  the  shocks  may  be  repeated  at  uncertain  intervals  for 
days,  or  even  weeks,  together.  Be  this  as  it  may,  whether  the 
shocks  be  slight  or  strong,  few  or  many,  the  concussion,  as  will  be 
seen,  appears  to  originate  in  some  definite  locality,  and  at  some  dis- 
tance beneath  the  earth's  surface.  There  is,  then,  as  might  be 
anticipated,  a  marked  difference  in  the  phenomena,  according  as 


EARTHQUAKES  AND  THEIR  EFFECTS.  263 

the  center  from  which  a  disturbance  has  been  propagated  is  situated 
under  the  dry  land  or  in  the  earth's  crust  beneath  the  ocean.  Sup- 
pose— at  present  only  for  the  purpose  of  illustration — the  earth- 
quake to  be  caused  by  a  subterranean  explosion.  In  both  the  cases 
a  sound  wave  travels,  and  a  shock  is  transmitted  through  the  crust, 
but  in  the  former  one  these  continue  their  course  until  they  reach 
the  surface.  In  some  instances  the  noise  precedes,  in  others  it  suc- 
ceeds, the  tremor;  in  others  the  two  are  practically  simultaneous. 
It  is  variously  described  as  "  a  hollow  booming  sound,"  "  like  distant 
thunder,"  "  the  rolling  of  a  heavy  wagon,"  or  "  the  bellowing  of 


FIG.  108.— DIAGRAM  ILLUSTRATING  MALLET'S  THEORY  OF  THE  DIRECTION  OF 
MOVEMENT  FROM  AN  EARTHQUAKE  Focus. 

A,  Earthquake  focus,  or  center  of  impulse  ;  B,  Seismic  verticle.  The  lines  A  i,  A  i',  A  2,  A  if,  A  3,  A  y, 
represent  the  direction  of  the  movement  from  A.  The  position  of  circles  shows  the  depths  at  which 
the  shock  would  be  felt  at  the  same  time — /".  e.  the  particles  would  move  on  the  lines  c  c',  d  d',  and  so 
on,  as  if  these  were  sections  of  hollow  shells  placed  one  over  the  other.  The  wave  would  reach  the  sur- 
face first  at  B,  and  travel  from  it  north  and  south,  occurring  simultaneously  at  the  coseismic  points  i  and 
i',  2  and  2',  3  and  3'. 

bulls."  Assuming  the  earth's  surface  to  be  level  on  the  region  in 
question,  the  shock  is  first  felt  at  a  spot  directly  above  that  where 
the  disturbance  has  originated.  Here  it  acts  in  a  vertical  direction — 
buildings,  columns,  pavements,  all  things  resting  on  the  ground,  are 
jerked  or  lifted  quickly  upward.  So,  if  masonry  is  damaged,  the 
cracks  run  horizontally,  and  though  roofs  may  collapse,  and  colon- 
nades may  totter  with  the  vibration,  the  tendency  to  overthrow  them 
is  but  slight.  It  is  also  possible  that  an  impulse  may  be  set  up  in, 
and  a  sound  wave  communicated  to,  the  air  above  the  place  where 
the  shock  emerges  ;  these,  however,  are  usually  unimportant  phe- 
nomena, and  often  pass  unnoticed.  So  long  as  no  change  takes 
place  in  the  materials  of  the  crust  the  shock  travels  uniformly  out- 
ward from  the  focus  of  the  disturbance.  Hence  all  the  points  which 
lie  on  the  surface  of  a  sphere  described  about  this  focus  as  a  center 
will  be  simultaneously  and  correspondingly  affected.  It  follows, 
therefore,  as  a  glance  at  the  annexed  diagram  will  indicate,  that  the 


264 


THE   STORY  OF  OUR  PLANET. 


shock  appears  to  spread  outward  along  the  ground  in  a  circular  form 
from  the  point  *  where  it  has  been  first  perceived,  just  as  waves 
travel  on  the  surface  of  a  quiet  pool  when  a  stone  is  dropped  from  a 
height  into  the  water ;  but  as  the  circle  widens,  the  direction  is 
changed  in  which  the  impulse  seems  to  act.  The  uplift  produced 

by  the  shock  becomes  more  and 
more  oblique.  Thus  columns, 
chimneys,  spires  are  more  likely 
to  be  overthrown,  and  to  fall, 
either  forward  or  backward,  in  the 
direction  of  a  radius  of  this  circle. 
The  cracks  in  a  wall  are  no  longer 
horizontal,  but  pass  from  course  to 
course  of  masonry,  and  make  an 
angle  with  the  horizon,  which  be- 
comes higher  as  the  place  is  more 
remote  from  the  original  center  of 
disturbance.  If,  then,  a  number  of 
observations  be  obtained,  sufficient 
for  the  elimination  of  accidental 
variations  and  for  securing  trust- 
worthy averages,  a  very  simple  mathematical  calculation  suffices 
to  determine,  with  considerable  precision,  the  depth  at  which  the 
shock  originated.  Again,  if  careful  note  has  been  taken  of  the 
time  at  which  the  shock  has  been  felt  at  a  series  of  stations  lying 
at  different  distances  from  the  seismic  vertical,  the  rate  at  which 
the  wave  has  traveled  can  be  also  ascertained. 

If,  however,  the  place  where  the  shock  originated  is  beneath  the 
bottom  of  the  sea,  the  phenomena  of  an  earthquake  become  more 
complex.  Here  also  the  disturbance  emerges  vertically,  and  it 
communicates  a  shock  to  the  overlying  mass  of  water.  This  pro- 
duces a  great  sea  wave,  exactly  as  an  undulation  may  be  started  in 
the  water  filling  a  flat  pan  by  giving  a  sharp  tap  at  the  bottom. 
The  shock,  however,  also  continues  to  travel  through  the  earth's 
crust  beneath  the  sea  ;  but  the  disturbance  becomes  insufficient  to 
produce  any  appreciable  effect  on  the  overlying  water  so  long  as 
this  is  deep  ;  but  when  this  is  shallow,  as  the  shore  is  approached,  the 
shock  gives  rise  to  an  undulation  called  the  "  forced  sea  wave." 
We  can  often  observe,  as  we  walk  along  the  bank  of  a  pool,  that  a 


FIG.  109.— DIAGRAM  OF  SEISMIC 
CIRCLES. 

B,  Seismic  vertical  ;    i  i*,  2  2*,  3  3*,  4  4* 
Coseismic  points  on  the  circles. 


Generally  called  "  the  seismic  vertical." 


EARTHQUAKES  AND    THEIR  EFFECTS.  265 

fish,  in  darting  from  its  lurking  place,  indicates  its  path  by  a  rise  in 
the  water,  which  disappears  as  it  enters  the  deeper  parts.  A  similar 
effect,  but  in  reverse  order,  is  produced  by  the  earthquake  shock  as 
it  passes  under  the  shallow  water.  An  observer  standing  on  the 
shore  sees  a  wave  larger  than  usual  approaching,  which  rides,  as  it 
were,  on  the  back  of  the  shock,  and  breaks  on  the  land  just  in  its 
rear.  Immediately  afterward  he  feels  the  tremor,  and  perhaps  hears 
a  rumbling  noise.  After  taking  note  of  this,  if  he  be  a  prudent 
person,  and  the  coast  a  low  one,  he  will  betake  himself  as  quickly 
as  possible  to  some  fairly  high  ground  and  watch  the  course  of 
events.  The  shock  does  not  always  travel  through  the  earth  at  the 
same  pace,  because  this,  as  will  presently  be  shown,  depends  upon 
the  nature  of  the  rock ;  but  it  almost  invariably  outstrips  the  wave 
which  has  been  generated  in  the  open  ocean,  the  velocity  of  which 
is  about  1138  feet  a  second.  When  the  latter  reaches  the  land,  it  is 
far  more  formidable  than  the  wave  which  accompanied  the  shock. 
Rising  higher  as  it  comes  into  the  shallower  water,  the  huge  mass 
breaks  upon  the  coast,  sometimes  rushing  far  inland  like  a  sudden 
deluge,  bringing  death  and  destruction  in  its  reflux,  and  sweeping 
out  to  sea  the  corpses  of  men  and  cattle.  When  the  shock 
originates  as  last  described,  a  sound  wave  and  a  vibration  may  be 
communicated  from  the  original  focus  of  disturbance  through  the 
ocean  to  the  air  above  it.  This  phenomenon,  however,  generally  is 
unimportant,  and  frequently  is  not  noticed. 

In  the  British  Isles  earthquakes  are  by  no  means  uncommon, 
though,  happily,  they  have  rarely  done  any  serious  damage,  and 
only  in  very  few  cases  caused  loss  of  life.  They  are  rather  frequent 
in  certain  parts  of  Scotland,  especially  along  the  line  of  the  Great 
Glen  and  about  Comrie,  in  Perthshire.  Records  have  been  found 
of  more  than  three  hundred  and  fifty,  and,  doubtless,  many  more  of 
a  slighter  character  have  escaped  notice.  Buildings  were  more  or 
less  damaged  by  fifty-nine  of  these,  and  in  a  few  cases  persons  are 
said  to  have  been  killed.  The  earthquake  of  April  15  (?),  1185, 
seriously  injured  Lincoln  Cathedral,  and  one  in  the  following  year 
did  nearly  as  much  mischief ;  that  of  December  21,  1248,  damaged 
the  cathedrals  of  Wells  and  St.  David's.  In  1246,  1275,  1382,  1580, 
"  churches  were  thrown  down,"  but  the  most  severe  on  record  for 
four  centuries  occurred  on  April  22,  1884.*  The  focus  of  the  dis- 


*  It  is  described  and  discussed  in  an  admirable  and  exhaustive  report  by  Professor  R. 
Meldola  and  Mr.  W.  White  :   "  Report  on  the  East  Anglian  Earthquake  "  ("  Essex  Field 


266  THE   STORY  OF  OUR  PLANET. 

turbance  seems  to  have  been  situated  nearly  beneath  the  village  of 
Abberton,  in  Essex,  and  the  shock  was  felt  from  Brigg,  in  Lincoln- 
shire, to  Freshwater,  in  the  Isle  of  Wight,  and  from  Street,  in 
Somersetshire,  to  Ostend,  in  Belgium,  over  an  area  altogether  of 
full  50,000  square  miles  ;  but  the  damage  was  limited  to  a  compara- 
tively small  area  in  the  Eastern  Counties,  and  was  more  severe  on 
the  stiff  clay — the  London  Clay  of  geologists — than  on  the  drift 
and  alluvial  deposits.  Walls  were  cracked,  chimney  stacks  were 
shattered  and  occasionally  fell,  and  in  Colchester  the  upper  part  of 
a  slightly  built  spire  was  thrown  down.  Altogether  1200  to  1500 
buildings  were  damaged,  though  in  many  instances  the  injuries 
were  slight,  but  no  harm  was  done  to  life  or  limb.  The  shock, 
which  occurred  about  9.18  A.  M.,  appears  to  have  been  composite  in 
character,  two  oscillations  having  been  distinctly  noticed  by  some 
observers;  t  was  accompanied  by  a  rumbling  noise,  like  distant 
thunder.  It  traveled  at  a  rate  estimated  from  9000  to  10,000  feet 
a  second.  Data  sufficient  to  fix  the  position  of  the  focus  of  the 
disturbance  could  not  be  obtained,  but  it  was  very  probably  due  to 
a  movement  in  the  hard  and  ancient  rock  mass  which  is  known  to 
underlie,  at  a  depth  of  some  1000  or  1200  feet,  the  comparatively 
soft  chalk  and  later  rocks  of  East  Anglia. 

Far  more  terrible  than  any  such  disaster  ever  experienced  in 
the  British  Isles  was  the  earthquake  of  Charleston  in  1886.  South 
Carolina  appears  to  be  rather  subject  to  this  calamity,  for  a  descrip- 
tion of  severe  earthquakes  which  occurred  in  1812,  and  in  some 
cases  altered  the  level  of  the  land,  will  be  found  in  Sir  C.  Lyell's 
"Principles  of  Geology."*  In  the  early  summer  of  1886  several 
slight  tremors  occurred,  which,  however,  did  not  excite  much  atten- 
tion. More  distinct  shocks  were  felt  on  August  27  and  28,  and 
the  great  shock  occurred  in  the  evening  of  August  31.+  The 
atmosphere  that  afternoon  had  been  unusually  sultry  and  quiet,  the 
breeze  from  the  ocean,  which  generally  accompanied  the  rising  tide, 
was  almost  entirely  absent,  and  the  setting  sun  caused  little  glow  in 
the  sky.  "  As  the  hour  of  9.50  was  reached  there  was  suddenly 

Club,  Special  Memoirs,"  vol.  i.),  from  which  all  the  particulars  concerning  English 
earthquakes  have  been  taken. 

*  Ch.  xxviii. 

f  A  history  of  this  earthquake,  with  illustrations  of  the  effects  produced  and  a  very 
elaborate  discussion  of  the  observations,  by  Captain  C.  E.  Dutton,  is  printed  in  the  "  Ninth 
Annual  Report  of  the  United  States  Geological  Survey,"  from  which  the  particulars  given 
above  are  taken. 


EARTHQUAKES  AND    THEIR  EFFECTS.  z6^ 

heard  a  rushing,  roaring  sound,  compared  by  some  to  a  train  of  cars 
at  no  great  distance,  by  others  to  a  clatter  produced  by  two  or  more 
omnibuses  moving  at  a  rapid  rate  over  a  paved  street,  by  others, 
again,  to  an  escape  of  steam  from  a  boiler.  It  was  followed  immedi- 
ately by  a  thumping  and  beating  of  the  earth  underneath  the  houses, 
which  rocked  and  swayed  to  and  fro.  Furniture  was  violently 
moved  and  dashed  to  the  floor;  pictures  were  swung  from  the 
walls,  and  in  some  cases  turned  with  their  backs  to  the  front,  and 
every  movable  thing  was  thrown  into  extraordinary  convulsions. 
The  greatest  intensity  of  the  shock  is  considered  to  have  been 
during  the  first  half,  and  it  was  probably  then,  during  the  period 
of  the  greatest  sway,  that  so  many  chimneys  were  broken  off 
at  the  junction  with  the  roof.*  .  .  The  duration  of  this  severe 
shock  is  thought  to  have  been  from  thirty-five  to  forty  seconds. 
The  impression  produced  upon  many  was  that  it  could  be  sub- 
divided into  three  distinct  movements,  while  others  were  of  the 
opinion  that  it  was  one  continuous  movement,  or  succession  of 
waves,  with  the  period  of  greatest  intensity,  as  already  stated,  during 
the  first  half  of  its  duration."  f  Twenty-seven  persons  were  killed 
outright,  and  more  than  that  number  died  soon  after  of  their  hurts 
or  from  exposure  ;  many  others  were  less  seriously  injured.  Among 
the  buildings  the  havoc,  though  much  less  disastrous  than  has  been 
recorded  in  some  other  earthquakes  in  either  hemisphere,  was  very 
great.  "  There  was  not  a  building  in  the  city  which  had  wholly 
escaped  serious  injury.  The  extent  of  the  damage  varied  greatly, 
ranging  from  total  demolition  down  to  the  loss  of  chimney  tops  and 
the  dislodgment  of  more  or  less  plastering.  The  number  of  build- 
ings which  were  completely  demolished  and  leveled  to  the  ground 
was  not  great ;  but  there  were  several  hundred  which  lost  a  large 
portion  of  their  walls.  There  were  very  many  also  which  remained 
standing,  but  so  badly  shattered  that  public  safety  required  that 
they  should  be  pulled  down  altogether.  There  was  not,  so  far  as  at 
present  known,  a  brick  or  stone  building  which  was  not  more  or 
less  cracked,  and  in  most  of  them  the  cracks  were  a  permanent  dis- 
figurement and  a  source  of  danger  and  inconvenience."  In  some 
places  the  railway  track  was  curiously  distorted.  "It  was  often 
displaced  laterally,  and  sometimes  alternately  depressed  and  elevated. 

;_   *  The  number  was  counted  afterward,  and  found  to  be  almost  14,000. 

f  "  Report,"  p.  231,  from  an  account  contributed  by  Dr.  Manigault.  An  account  is 
also  printed  from  the  pen  of  one  of  the  staff  of  the  Charleston  News  and  Courier,  which 
supplies,  perhaps  with  a  little  picturesque  coloring,  many  interesting  minor  details. 


268  THE   STORY  OF  OUR  PLANET. 

Occasionally  severe  lateral  flexures  of  double  curvature  and  of  great 
amount  were  exhibited.  Many  hundred  yards  of  track  had  been 
shoved  bodily  to  the  south  eastward." 

At  Charleston  the  ground  was  fissured  in  places  to  a  depth  of 


FIG.  no.— STREET  HOUSES  IN  CHARLESTON  DAMAGED  IN  THE  SOUTH  CAROLINA 
EARTHQUAKE  OF  1886. 


many  feet,  and  numerous  "  craterlets "  were  formed,  from  which 
sand  was  ejected  in  considerable  quantities.  Both  these  phenomena 
are  not  unusual  in  earthquakes.  During  one  which  occurred  in 
New  Zealand  in  1825  a  cleft  opened  which  could  be  traced  for  about 
ninety  miles,  the  ground  in  one  part  being  permanently  upraised 
to  a  height  of  as  much  as  nine  feet.  Similar  fissures  and  craterlets 
were  formed  in  South  Carolina  during  the  earthquakes  of  1811-12, 


EARTHQUAKES  AND    THEIR  EFFECTS.  269 

as  well  as  in  those  which  devastated  Calabria  in  1783.  The  crater- 
lets  are  due,  no  doubt,  to  the  squirting  out  of  water  from  saturated 
sandy  layers  not  far  below  the  surface,  as  they  are  squeezed  between 
two  less  pervious  beds  by  the  passage  of  the  wave.  The  ejected 
material  in  the  Charleston  earthquake  was  ordinary  sand,  such  as 
might  have  been  obtained  in  many  districts  which  have  been  quite 
undisturbed  by  any  concussions  of  the  earth. 

Captain  Button  has  made  a  careful  study  of  the  observations  col- 
lected by  himself  and  others,  and  has  come  to  the  conclusion  that 
the  Charleston  wave  traveled  with  unusual  speed,  for  its  mean 
velocity  was  about  17,000  feet  a  second.*  The  focus  of  the  dis- 
turbance was  also  ascertained.  Apparently  it  was  a  double  one,  the 
two  centers  being  about  thirteen  miles  apart,  and  the  line  joining 
them  running  nearly  the  same  distance  to  the  west  of  Charleston. 
The  approximate  depth  of  the  principal  focus  is  given  as  twelve 
miles,  with  a  possible  error  of  less  than  two  miles  ;  that  of  the  minor 
one  as  roughly  eight  miles. 

In  Japan,  which  might  almost  be  called  a  land  of  earthquakes,  for 
in  the  year  1888  no  less  than  630  shocks  were  observed,  similar 
results,  on  a  yet  greater  scale,  were  produced  by  the  terrible  shock 
of  October  28,  1891.  Professor  Milne,  who  for  some  years  past 
has  carefully  studied  the  earthquakes  of  Japan,  has  recently  de- 
scribed the  effects  and  published  photographs  of  certain  of  the  more 
remarkable.f  On  this  occasion  the  tremors  lasted  for  some  minutes. 
At  Tokio  the  earth  rocked,  the  water  in  a  tank  was  splashed  over 
the  edge,  the  trees' were  swinging  about,  the  telegraph  wires  were 
clattering  together,  and  the  effect  of  the  motion  was  to  make  him 
feel  giddy  and  slightly  seasick.  Chimneys  fell,  houses,  temples, 
and  factories  were  shattered,  bridges  were  broken,  roads  and  rail- 
ways distorted  by  vertical  and  lateral  twists,  several  embankments 
destroyed,  the  ground  was  fissured  in  all  directions,  and  mountain 
sides  slipped  down  and  blocked  the  valleys.  The  disturbance, 
according  to  Dr.  B.  Koto,  is  connected  with  the  formation  of  a 
great  fault  which  can  be  traced  on  the  surface  of  the  earth  for  a 
distance  of  between  forty  and  fifty  miles.  "  In  the  Neo  valley,  where 
it  runs  nearly  north  and  south,  it  looks  like  one  side  of  a  railway 
embankment  about  twenty  or  thirty  feet  in  height.  The  fields  at 

*The  mean  of  the  calculations  amounted  to  17,008  feet  a  second,  with  262  feet  as  the 
probable  limit  of  error. 

f  Milne  and  Burton,  "  The  Great  Earthquake  in  Japan."  See  also  "  British  Association 
Report,"  1892,  p.  93. 


2 yo  THE   STORY  OF  OUR  PLANET. 

the  bottom  of  this  ridge  were  formerly  level  with  the  fields  now  at 
the  top  of  it."*  Along  this  line  horizontal  displacements  also  have 
been  noticed.  Here  plots  of  land  once  adjacent  have  been  parted  ; 
there  the  ground  has  been  actually  compressed,  and  the  breadth  of 
a  tract  been  diminished  by  half  a  dozen  yards.  Since  the  great  shock 


FIG.  in. — FISSURE  PRODUCED  BY  AN  EARTHQUAKE,  BELLA,  CALABRIA. 
(After  Mallet) 

about  3000  minor  shakings  have  been  noticed,  with  the  result  that 
"in  an  area  of  4176  square  miles,  which  embraces  one  of  the  most 
fertile  plains  of  Japan,  and  where  there  is  a  population  of  perhaps 
1000  to  the  square  mile,  all  the  buildings  which  had  not  been 
reduced  to  a  heap  of  rubbish  had  been  badly  shattered.  To  rebuild 
the  railway,  reconstruct  bridges,  roads,  and  embankments,  and  to 


*"  British  Association  Report,"  1892,  p.  117. 


EARTHQUAKES  AND    THEIR  EFFECTS.  271 

relieve  immediate  distress,  about  one  and  three-quarters  million 
pounds  sterling  have  been  poured  into  the  district,  the  greater  por- 
tion of  which  came  from  the  Imperial  Treasury.  This  sum,  however, 
only  measures  a  fraction  of  the  total  destruction.  One  hundred 
thousand  homes  have  yet  to  be  rebuilt ;  irrigation  works  have  to  be 
repaired  ;  a  value  has  to  be  given  to  land  which  has  been  buried  by 
landslides,  or  lost  by  what  appears  to  be  a  permanent  compression 
of  valleys ;  there  has  been  a  six  months'  interruption  of  traffic  and 
industries,  and  nearly  10,000  people  have  lost  their  lives." 

The  Nagoya-Gifu  district,  where  the  earthquake  was  very  severe, 
is  a  flat  expanse  of  rich  alluvium,  fringed  on  its  east  and  west  sides 
by  low  hills  of  comparatively  incoherent  and,  geologically,  rather 
recent  materials.  These  lie  at  the  foot  of  a  mountain  range  which 
rises  to  a  height  of  from  2000  to  4000  feet,  and  consists  of  slates, 
limestones,  and  crystalline  rocks,  without  any  signs  of  volcanic 
action. 

Among  modern  earthquakes  one  which  occurred  in  Ischia  on 
March  4,  1881,  presented  some  peculiarities.  The  shock  was  severe, 
for  many  houses  were  destroyed,  and  127  persons  were  either  killed 
on  the  spot  or  died  of  their  injuries,  but  the  area  over  which  it  pro- 
duced any  sensible  effect  was  very  limited.  At  Naples  it  was  not 
felt,  and  even  at  Capo  di  Miseno,  only  some  eight  miles  away,  it 
was  barely  noticed.  The  focus  of  disturbance  was  evidently  beneath 
a  part  of  the  island ;  the  roofs  and  floors  of  houses  in  Casamenella 
collapsed,  but  the  walls  were  not  generally  thrown  down  ;  around 
this  area  the  angle  of  emergence  of  the  shock  rapidly  diminished. 
Obviously,  then,  the  disturbance  must  have  originated  near  to  the 
surface.  It  was  probably  connected  with  Monte  Epomeo,  the  cul- 
minating point  of  the  island,  which  is  a  ruined  crater,  extinct  itself, 
though  eruptions  from  parasitic  cones  have  occurred  in  historic 
times.  A  second  very  disastrous  earthquake  occurred  on  July  28, 
1883,  by  which  a  somewhat  larger  area  was  affected.*  Jschia  obvi- 
ously, notwithstanding  other  attractions,  is  not  a  desirable  place  of 
residence,  for  a  day  may  come  when  Monte  Epomeo  may  repeat  the 
kind  of  performance  by  which  Vesuvius  some  eighteen  centuries 
since  celebrated  its  return  to  the  list  of  active  volcanoes. 

Among  the  less  recent  earthquakes  that  of  Caracas  is  noted  for 
the  frightful  destruction  of  life  and  property.  On  March  26,  1812, 
"  several  violent  shocks  of  an  earthquake  were  felt.  The  surface 

*  '   British  Association  Report,"  1883,  pp.  409,  501. 


272  THE    STORY   OF   OUR  PLANET. 

undulated  like  a  boiling  liquid,  and  terrrific  sounds  were  heard 
underground.  The  whole  city,  with  its  splendid  churches,  was  in 
an  instant  a  heap  of  ruins,  under  which  10,000  of  the  inhabitants 
were  buried."*  The  earthquake  of  Lisbon  in  1755  produced  con- 
sequences yet  more  disastrous.  "  The  inhabitants  had  no  warning 
of  the  coming  danger,  when  a  sound  like  thunder  was  heard  under- 
ground, and  immediately  afterward  a  violent  shock  threw  down  the 
greater  part  of  their  city."  Numbers  of  persons  were  buried  beneath 
the  ruins ;  many  of  the  survivors  rushed  toward  the  quays,  but  the 
sea  first  retired  and  then  rolled  in,  rising  50  feet  or  so  above  its 
ordinary  level.  On  one  quay,  which  had  been  recently  built  at  a  very 
heavy  expense,  "  a  great  concourse  of  people  had  collected  there  for 
safety,  as  a  spot  where  they  might  be  beyond  the  reach  of  falling 
ruins  ;  but  suddenly  the  quay  sank  down  with  all  the  people  on  it, 
and  not  one  of  the  dead  bodies  ever  floated  to  the  surface.  A  great 
number  of  boats  and  small  vessels  anchored  near  it,  all  full  of 
people,  were  swallowed  up  as  in  a  whirlpool.  No  fragments  of 
these  wrecks  ever  rose  again  to  the  surface."  The  account  of  this 
catastrophe,  as  Sir  C.  Lyell  observes,f  is  clearly  exaggerated,  and 
the  disappearance  of  the  pier  seems  almost  unaccountable,  for  the 
depth  of  that  part  of  the  Tagus,  even  at  high  tide,  does  not  exceed 
30  feet.  He  suggests  that  possibly  a  deep  narrow  chasm  may  have 
opened  in  the  bed  of  the  estuary  and  closed  again  after  swallowing 
up  some  vessels  and  adjoining  buildings.  If  so,  this  must  have 
been  the  result  of  a  second  shock,  for  some  minutes  had  elapsed 
evidently  since  the  first  one,  as  the  people  had  collected  on  the 
quay.  Possibly  the  following  may  be  the  true  explanation  :  The 
strata  near  the  river  appear  to  consist  of  rather  loose  and  incoherent 
materials.  By  the  first  shock  these  may  have  been  disturbed,  and 
the  foundations  of  the  pier  so  seriously  shaken  that  its  stability  was 
destroyed.  Hence,  when  the  great  sea  wave  rushed  upon  it,  the 
whole  mass  of  masonry,  with  the  clayey  substructure  on  which  it 
rested,  may  have  slipped  bodily  forward  into  the  water,  and  the 
shattered  fragments  of  the  pier,  with  the  submerged  vessels  and  the 
drowned  bodies,  may  have  been  entombed  in  the  fluid  mud  which 
would  be  stirred  up  by  the  catastrophe.  The  landslip  at  Zug  in 
1887,  visited  by  myself,  illustrates  the  manner  in  which  I  conceive 
the  disaster  to  have  occurred.  A  broad  strip  of  land  bordering  the 


*  Lyell,  "  Principles  of  Geology,"  ch.  xxviii. 
f  Ibid.,  ch.  xxx. 


EARTHQUAKES  AND    THEIR  EFFECTS.  273 

lake  had  slipped  suddenly  forward  into  the  water.  The  houses  upon 
it  were  reduced  to  mounds  of  brickwork,  here  and  there  rising  above 
the  surface.  The  debris  of  the  land,  with  part  of  the  bed  of  the 
lake,  appeared  to  have  glided  outward,  so  that  the  disturbance 
extended  for  above  a  thousand  yards  from  the  shore.* 

Not  the  least  remarkable  feature  in  the  earthquake  of  Lisbon  was 
the  unusually  large  area  over  which  the  shock  was  felt.  According 
to  Humboldt  this  was  four  times  greater  than  the  extent  of  Europe. 
The  earlier  statements,  however,  appear  to  be  exaggerated,  for  all 
disturbances  which  occurred  about  the  same  date  were  at  once  set 
down  to  the  convulsion  which  shattered  Lisbon.  Thus  it  may  be 
doubted  whether  this  earthquake  shook  New  York  or  disturbed  the 
waters  of  Ontario,  or,  indeed,  was  felt  anywhere  in  North  America, 
though  the  sea  wave  which  it  originated  does  appear  to  have 
crossed  the  Atlantic  and  dashed  upon  the  coasts  of  Barbadoes  and 
Martinique,  where  the  water  rose  a  dozen  feet  or  more  above  its 
usual  tidal  level.  But  the  shock  was  certainly  felt  over  an  area  at 
least  six  times  the  size  of  France,  and  is  generally  believed  to  have 
been  sensible  in  Scotland,  where  the  water  of  Loch  Lomond  rose 
and  fell  for  rather  more  than  two  feet.  In  England  it  was  un- 
noticed, doubtless  for  this  reason  :  the  shock  probably  originated 
in  hard  and  ancient  rocks,  through  which  its  main  influence  would 
be  propagated.  These,  in  the  eastern  part  of  England,  lie  at  a  con- 
siderable depth — generally  full  a  thousand  feet  below  the  surface — 
and  are  covered  up  with  less  coherent  materials,  but  they  emerge  to 
the  air  in  Scotland.  The  shock,  of  course,  as  it  traveled  would  be 
communicated  to  the  overlying  rocks,  but  among  them  its  effects 
would  be  speedily  dissipated  ;  just  as  slight  vibrations  in  a  bed- 
stead would  not  affect  anyone  upon  it  if  he  lay  on  the  top  of  a 
thick  feather  bed 

No  district,  however,  in  Europe  has  a  worse  repute  for  earth- 
quakes than  Calabria,  and  in  none  have  they  been  more  carefully 
studied.  From  1783  to  1786  the  shocks  were  frequently  repeated  ; 
the  land  suffered  from  an  epidemic  of  tremors.  In  the  former  year 
949  shocks  were  observed,  and  151  in  the  year  following.  The 
district  was  visited  by  a  deputation  from  the  Royal  Academy  of 
Naples,  and  by  other  men  of  science,  including  Sir  W.  Hamilton, 
who  made  careful  observations,  which  were  afterward  published. 
Again,  in  1857  Calabria  passed  through  another  phase  of  earth- 

*  Nature,  vol.  xxxvi.  p.  389  ;  also  vol.  xxxviii.  p.  268. 


274 


THE    STORY   OF  OUR  PLANET. 


quakes ;  these  were  studied  by  Mr.  Mallet,  and  described  in  his 
well-known  work.*  The  region  affected  consists  partly  of  thick 
clayey  strata,  associated  with  occasional  beds  of  sand  and  limestone 
deposits,  all  comparatively  incoherent,  partly  of  harder  and  more 
schistose  rocks,  and  of  granite ;  these  rise  from  beneath  the  others 


FIG.  112. — CATHEDRAL  OF  TITO,  CALABRIA,  AFTER  THE  EARTHQUAKE  OF  1857. 
(After  Mallet.} 

to  form  the  mountainous  district,  a  prolongation  of  the  Apennines. 
In  the  earlier  earthquakes  the  worst  shocks  appear  to  have  occurred 
on  February  5  and  on  March  28,  1783.  The  region,  however,  which 
was  very  seriously  affected  was  not  large,  for  its  area  was  only 
about  500  square  miles.  "  If  the  city  of  Oppido,  in  Calabria  Ultra, 
be  taken  as  a  center,  and  round  that  center  a  circle  be  described 
with  a  radius  of  twenty-two  miles,  this  space  will  comprehend  the 
surface  of  the  country  which  suffered  the  greatest  alteration,  and 
where  all  the  towns  and  villages  were  destroyed."  f  At  times  the 
surface  of  the  land  seemed  to  heave  "  like  the  billows  of  a  swelling 
sea  .  .  .  trees,  supported  by  their  trunks,  sometimes  bent  during 


*  "  The  Neapolitan  Earthquake  of  1857." 
f  Lyell,  "  Principles  of  Geology,"  ch.  xxix. 


EARTHQUAKES  AND    THEIR  EFFECTS. 


275 


the  shocks  to  the  earth,  and  touched  it  with  their  tops  "  ;  water  and 
sand  were  discharged  from  craterlets,  as  above  described,  fissures 
opened  in  the  ground,*  changes  of  level  occurred,  and  landslips 


FIG.  113. — STREET  VIEW  IN  LA  POLLA  AFTER  THE  EARTHQUAKE  OF  1857. 

were  numerous  and  formidable.  The  shocks  were  exceptionally 
destructive  to  property  in  consequence  of  a  peculiarity  in  the 
geological  structure  of  the  country.  In  the  lower  parts  of  the 
valleys  in  the  hill  districts  the  incoherent  clays  mentioned  above 
rest  upon  the  older  and  harder  rocks,  having  been  deposited  upon 
them,  after  the  broad  outlines  of  the  physical  structure  of  the 
country  had  been  produced,  as  muds  might  be  laid  down  at  the 
present  day  in  a  sea  loch  or  estuary  on  the  Scottish  coast.  After 


*  These  are  said  to  have  yawned  wide  enough  to  engulf  houses,  on  which  they  some- 
times closed.  It  is  possible,  however,  that  in  some  cases  the  phenomena  described  may 
be  not  so  much  the  direct  result  of  a  fissuring  of  the  ground  under  the  strain  caused  by  the 
passage  of  an  earthquake  wave  as  the  consequence  of  a  slipping  of  the  mass,  when  its 
tension  would  be  much  greater,  and  large  cracks  would  open  and  close  as  it  moved  along. 


276  THE   STORY  OF  OUR  PLANET. 

the  land  had  been  elevated  above  the  sea,  streamlets  cut  deep 
gashes  into  these  clays,  and  rivers  washed  away  large  portions, 
leaving  the  remainder  in  insulated  masses,  projecting  outward  from 
the  mountain  flanks  and  sloping  steeply  down  to  the  present  beds 
of  the  valleys.  These  flat-topped  bastions,  from  their  obvious 
natural  advantages,  had  become  the  favorite  site  for  villages ;  but  in 
them  the  buildings  suffered  much  more  severely  than  in  those  on 
the  harder  rock.  The  shock  travels  more  slowly  through  inco- 
herent than  through  solid  materials,  and  so  produces  usually  more 
serious  consequences.  The  change  also  in  the  character  of  the 
rock  is  apt  to  cause  secondary  or  reflected  shocks  near  the  junction, 
and  in  this  case  the  peculiar  configuration  of  the  surface  facilitated 
actual  landslips  and  settlements  in  the  less  coherent  materials.  A 
village  thus  situated  may  crumble  into  ruins  as  the  shudder  passes 
through  the  ground.  In  some  places  even  huge  masses  of  cliff  or 
portions  of  a  hillside  fell  or  slipped  bodily  away.  On  the  coast  the 
terrible  sea  wave  more  than  once  swept  in  and  inundated  the  low- 
lands. Near  Scylla,  of  classic  fame,  its  "  dogs  of  death  "  swooped 
down,  and  might  be  said  to  have  joined  hands  with  Charybdis.  On 
the  night  of  February  5  the  people,  at  the  advice  of  their  prince, 
had  taken  refuge  in  their  boats.  Suddenly,  after  a  terrible  con- 
vulsion, a  huge  wave  rolled  in  upon  the  land,  and  then  swept  back 
to  sea.  Every  boat  was  swamped  or  wrecked  ;  the  prince,  with 
1430  of  his  people,  perished. 

The  observers  of  some  of  the  earlier  earthquakes  believed  that 
the  ground  was  occasionally  affected  by  an  eddying  movement. 
This  idea,  which  in  itself  does  not  appear  to  be  very  intelligible, 
was  effectually  disposed  of  by  Mr.  Mallet,  who  showed  that  the 
lateral  displacement  which  the  stones  suffered  in  certain  structures 
was  simply  the  effect  of  an  ordinary  shock,  and  could  be  explained 
by  well-known  mechanical  laws.  He  obtained  a  large  number  of 
observations,  from  which  he  calculated  that  the  depth  of  the  focus 
of  disturbance  in  1857  did  not  exceed  seven  or  eight  miles,  and  per- 
haps was  not  more  than  five. 

Two  earthquakes  of  great  severity,  which  occurred  during  the 
present  century,  within  three  years  one  of  another,  are  remarkable 
for  producing  an  unusual  and  extensive  alteration  in  the  level  of 
the  ground.  The  one,  which  happened  on  June  16,  1819,  chiefly 
affected  the  province  of  Cutch,  especially  in  the  neighborhood  of 
the  eastern  channel  of  the  Indus ;  but  its  vibrations  were  felt  inland 
in  various  directions  to  a  distance  of  1000  miles  from  the  chief  seat 


EARTHQUAKES  AND    THEIR  EFFECTS.  277 

of  the  disturbance.  Towns  were  ruined  and  rocks  shaken  down 
from  the  hills,  but  the  most  remarkable  changes  were  in  the  Runn 
of  Cutch,  an  enormous  salt  marsh  larger  than  Yorkshire,  which  runs 
back  for  a  long  distance  inland  from  the  hea.d  of  the  Gulf  of  Cutch. 
It  is  flooded  by  the  sea  at  certain  states  of  the  tide  and  wind,  and  is 
traversed  on  its  western  side  by  a  channel  of  the  Indus.  This,  prior 
to  the  earthquake,  could  be  forded  at  a  place  called  Luckput,  for 
the  depth  at  low  water  was  only  about  a  foot ;  even  at  high  water 
it  did  not  exceed  a  couple  of  yards.  After  the  shock  the  depth 
was  increased  to  18  feet  at  low  water.  "  By  this  and  other  remark- 
able changes  of  level  a  part  of  the  inland  navigation  of  that  country, 
which  had  been  closed  for  centuries,  became  again  practicable.  Not 
less  marked  results  were  produced  at  Sindree,  a  village  above 
Luckput.  Here  a  fort  stood  near  the  water  side  and  a  few  feet 
above  it.*  From  one  angle  a  massive  circular  tower,  like  the  keep 
of  a  European  castle,  rose  to  some  height  above  the  general  level  of 
the  walls  and  smaller  towers.  After  the  shock  the  sea  rushed  up 
the  eastern  mouth  of  the  Indus  and  permanently  flooded  an  area  of 
land  about  2000  square  miles  in  extent.  The  village  of  Sindree 
disappeared,  the  fort  was  almost  submerged,  only  the  top  courses 
of  its  walls  and  the  upper  part  of  the  "  keep  "  projecting  from  the 
wide  expanse  of  water.  This,  nowever,  was  not  the  sole  change  ; 
the  subsidence  was  to  some  extent  compensated  by  elevation. 
The  inhabitants  of  Sindree  sav^ed  themselves  by  taking  refuge  on 
the  top  of  the  "  keep,"  and  from  it  they  saw,  "  at  the  distance  of  five 
and  a  half  miles  from  their  village,  a  long  elevated  mound,  where 
previously  there  had  been  a  low  and  perfectly  level  plain.  To  this 
uplifted  tract  they  gave  the  name  of  Ullah  Bund,  or  the  '  Mound  of 
God,'  to  distinguish  it  from  several  artificial  dams  thrown  across  the 
eastern  arm  of  the  Indus."  Its  extent  from  east  to  west — that  is, 
parallel  to  the  line  of  the  main  subsidence — was  more  than  fifty 
miles,  its  breadth  at  the  widest  part  was  about  sixteen  miles,  and 
its  greatest  elevation  above  the  original  level  was  ten  feet.  This 
height  was  maintained  over  a  large  portion  of  the  mound.  During 
the  next  few  years  after  the  earthquake  the  Indus  made  consid- 
erable variations  in  its  course — among  other  things  cutting  through 
the  Ullah  Bund — but  the  change  in  level  appears  to  have  been  per- 


*In  the  "  Principles  of  Geology,"  ch.  xxviii.,  two  sketches  are  compared,  which  show 
the  place  before  and  after  the  earthquake.  Reference  to  this  earthquake  has  been  already 
made  on  p.  204. 


278  THE    STORY  OF  OUR  PLANET. 

manent,  and  a  further  subsidence  in  the  Runn,  according  to  Sir  C. 
Lyell,  occurred  after  an  earthquake  in  June,  1845. 

The  coast  of  Chili,  on  November  19,  1822,  was  shaken  by  a 
violent  earthquake.  It  affected  a  very  large  area,  but  was  especially 
destructive  at  Valparaiso,  St.  Jago,  and  Quintero.  Several  of  the 
phenomena  already  mentioned  were  observed,  but  the  most  remark- 
able was  the  permanent  uplifting  of  a  considerable  tract  of  the 
South  American  coast  to  a  height  of  from  three  to  four  feet.  Rocks 
with  oysters  and  other  mollusks,  or  with  beds  of  seaweed  still 
attached,  were  raised  above  the  sea,  and  the  change  appears  to  have 
been  permanent.  That  it  was  not  the  first  movement  in  an  upward 
direction  is  indicated  by  "  several  older  elevated  lines  of  beach,  one 
above  the  other,  consisting  of  shingle  mixed  with  shells,  extending 
in  a  parallel  direction  to  the  shore,  to  the  height  of  50  feet  above 
the  sea."  *  According  to  Mr.  Darwin  and  Captain  Fitzroy,f  the 
same  region  was  further  elevated  by  an  earthquake  which  occurred 
on  February  20,  1835.  "The  southern  end  of  the  island  of  St. 
Mary  was  uplifted  eight  feet,  the  central  part  nine,  and  the  northern 
end  ten  feet,  and  the  whole  island  more  than  the  surrounding  districts. 
Great  beds  of  mussels,  patellae,  and  chitons,  still  adhering  to  the 
rocks,  were  upraised  above  high  water  mark  ;  and  some  acres  of  a 
rocky  flat,  which  was  formerly  always  covered  by  the  sea,  were  left 
standing  dry,  and  exhaled  an  offensive  smell  from  the  many  attached 
and  putrefying  shells."  In  this  case  the  elevation  appears  not  to 
have  been  altogether  permanent,  for  the  land  in  the  course  of  some 
weeks  subsided  for  four  or  five  feet.  But  Mr.  Darwin's  observations 
of  this  coast  clearly  indicate  that  a  very  long  strip  of  it  (doubtless 
associated  with  a  considerable  part  of  the  parallel  mountain  chain 
of  the  Andes)  has  been  upraised  by  successive  movements,  within 
comparatively  recent  times,  to  a  height  which  is  sometimes  not 
less  than  40x3  feet. 

Observations  of  the  rate  at  which  an  earthquake  shock  travels 
give  very  different  results.  Some  years  since  a  series  of  experiments 
was  made  by  the  late  Mr.  Mallet  in  order  to  ascertain  the  probable 
velocities  of  propagation  on  the  hypothesis  that  the  time  of  transit 
stands  in  a  certain  relation  to  the  elasticity  of  the  rock.  The 
results  thus  obtained  gave  figures  ranging  from  3640  feet  a  second 
in  a  limestone  from  the  Lias,  to  12,757  feet  m  a  slate  from  Charn- 

*  "  Principles  of  Geology,"  ch.  xxviii. 

f  "  Geological  Observations,"  part  ii.  ch.  ix. ;  "  Voyages  of  Adventure  in  the  Beagle" 
vol.  ii.  p.  415. 


EARTHQUAKES  AND    THEIK  EFFECTS.  279 

wood.  In  the  harder  limestones  the  velocity  was  from  nearly  six 
to  about  seven  thousand  feet  a  second.  These  results,  however, 
assumed  the  rock  to  be  solid,  and  not  traversed  by  cracks,  joints,  or 
divisional  surfaces  of  any  kind,  so  that  in  each  case  they  would  be  in 
excess  of  the  truth.  The  results  deduced  from  actual  observation 
are  yet  more  diverse.  A  shock  produced  by  an  explosion  of  gun- 
powder at  Holyhead  was  observed  by  Mr.  Mallet  to  travel  at  the 
rate  of  almost  825  feet  a  second  in  wet  sand,  and  of  about  1665 
feet  in  solid  granite ;  and  disturbances  produced  by  exploding 
dynamite,  observed  by  Professor  J.  Milne,  in  Japan,  went  even 
slower — viz.,  from  200  to  630  feet  a  second.  The  rate  of  an  earth- 
quake wave  at  Travancore  was  as  low  as  656  feet  a  second  ;  that  in 
the  Calabrian  earthquake  of  1857  only  789;  that  of  Herzogenrath, 
in  1877,  had  a  velocity  of  1555  feet,  and  that  in  the  Pennine  Alps, 
in  1855,  traveled  as  far  as  Turin  at  the  average  rate  of  1398  feet  a 
second,  and  to  Strasburg  at  that  of  2861  feet,  while  one  in  Central 
Europe,  in  1872,  gave  a  rate  of  2433.  Earthquake  shocks  in  Japan 
have  traveled  on  different  occasions  at  about  5100,  8000,  and  9800 
feet  a  second.  But  the  velocity  of  the  Charleston  earthquake,  as 
already  stated,  amounted  to  17,008  feet  a  second — a  pace  unac- 
countably rapid ;  but  the  result  is  supported  by  a  determination 
made  by  General  Abbott  at  the  destruction  of  Flood  Rock,  in  the 
United  States,  where  the  shock  traveled  at  the  rate  of  20,526  feet  a 
second.  Professor  J.  Milne  has  come  to  the  conclusion  that  the 
velocity  of  transit  decreases  as  a  disturbance  radiates,  and  varies 
with  the  initial  intensity  of  the  disturbance.* 

Of  late  years  the  more  careful  study  and  record  of  earthquakes 
have  led  to  some  interesting  results.  It  is  now  probable  that  they 
occur  more  frequently  at  certain  seasons  of  the  year  and  hours  of 
the  day.  Of  1230  earthquakes  observed  in  Switzerland,f  only  435, 
or  just  over  35  per  cent.,  happened  in  the  six  months'  period  from 
April  to  September  inclusive  ;  the  smallest  number  of  shocks  (40) 
was  in  July;  the  largest  (165)  in  December,  and  from  the  one  to 
the  other  there  was  a  fairly  regular  increase.  May,  June,  July,  and 
August  were  comparatively  quiet  months,  the  total  number  of 
shocks  registered  during  these  being  199;  December,  January, 
February,  and  March  were  correspondingly  disturbed,  599  shocks 
occurring  in  this  period.  Between  August  and  September  the 


*  "  British  Association  Report,"  1892,  p.  127. 
f  Reclus  "  The  Earth,"  ch.  Ixxviii. 


EARTHQUAKES  AND  THEIR  EFFECTS.  281 

increase  is  marked,  and  the  decrease  is  not  less  so  between  April 
and  May.* 

Another  set  of  observations  leads  to  the  conclusion  that  earth- 
quakes are  lovers  of  darkness.  Of  502  recorded  in  Switzerland,  the 
times  of  which  are  known,  320,  or  64  per  cent.,  occurred  between 
6  p.  M.  and  6  A.  M.f  Some  have  thought  that  a  connection  can  be 
traced  between  the  frequency  of  earthquakes  and  of  sun  spots ;  but 
this,  until  more  data  have  been  ascertained,  cannot  be  regarded  as 
established.  Professor  G.  Darwin  has  pointed  out  that  the  pressure 
upon  large  areas  of  the  earth's  surface  must  be  considerably  modi- 
fied by  changes  in  the  level  of  the  ocean  due  to  the  tide.  When 
there  is  a  difference  of  five  yards  between  high  and  low  tide,  this 
means  the  addition  or  subtraction  of  a  pressure  of  more  than  seven 
pounds  to  the  square  inch,  or  about  half  an  atmosphere,  and  it  must 
be  remembered  that  the  fluctuations  in  the  pressure  of  the  atmos- 
phere itself,  when  operating  on  large  areas,  may  not  be  wholly  negli- 
gible, and  may  play  the  part  of  the  proverbial  last  ounce. 

But  although  various  circumstances  more  or  less  external  may 
possibly  have  an  indirect  influence  upon  the  occurrence  of  earth- 
quakes, the  primary  cause  undoubtedly  must  be  sought  within  the 
crust  of  the  earth  itself.  The  depth  of  the  center  of  disturbance 
appears  not  to  exceed  about  thirty  miles,  and  is  very  commonly 
from  about  five  to  ten  miles,  and  a  study  of  a  chart  of  the  regions 
most  affected  by  earthquakes  leads  to  the  conclusion  that  they  are 
frequent  where  volcanoes  either  are  still  active  or  but  recently, 
geologically  speaking,  have  become  extinct  (Fig.  1 14).  They  are 
also  frequent  in  regions  which  are  distinctly  mountainous,  such  as 
the  Alps,  the  Apennines,  the  Andes,  the  Rocky  Mountains  ;  old  hill 
districts  also,  such  as  the  Scotch  Highlands  and  part  of  the  Spanish 
peninsula,  are  commonly  disturbed.  Not  seldom  the  two  apparent 
causes  are  united  in  the  same  region,  as  in  New  Zealand  and  in 
Japan,  where  earthquakes  are  chronic  ;  though,  according  to  Profes- 
sor J.  Milne,  the  majority  of  those  which  he  has  observed  in  that 
country  do  not  come  from  the  volcanoes,  nor  do  they  seem  to  have 
any  direct  connection  with  them.  We  can  readily  understand  that 
in  a  volcanic  region  the  earth's  crust  may  be  sometimes  shaken  by 

*  Professor  J.  Milne's  observations  of  101  earthquakes  felt  in  1888,  at  Tokio,  show  an 
irregular  distribution,  and  hardly  any  difference. — "  British  Association  Reports,"  1892, 
p.  98. 

f  This  also  is  not  borne  out  by  Professor  Milne's  observations,  the  difference  being 
small,  but  the  after-midnight  hours  are  slightly  the  less  disturbed. — Ibid.,  p.  99. 


282  T&E   STORY  OF  OUR  PLANET. 

the  subterranean  explosion  of  gases,  or  may  be  rent  asunder  by  the 
pressure  of  a  mass  of  lava  as  it  forces  its  way  underground,  or  may 
tremble  from  the  sudden  subsidence  of  strata  which  have  been  left 
unsupported  by  the  condensation  of  vapor.  The  explosion  of  a 
powder  barge  at  Erith,  on  October  I,  1864,  made  the  ground  quiver 
slightly  even  at -Cambridge;  and  when  10,000  pounds  weight  of  gun- 
powder blew  up  in  the  mills  at  Mainz,  the  tremor  was  felt  more  than 
a  hundred  miles  away.  In  mountain  regions  also,  and  wherever 
rocks  are  being  either  bent  into  folds  or  broken  by  faults,  large 
masses  may  yield  suddenly  to  strains,  and  so  produce  sometimes  a 
tremor  which  merely  suffices  to  agitate  a  seismometer,  sometimes  a 
shock  which  shatters  a  city.  As  important  landslips  on  the  surface 
often  cause  the  ground  to  quiver  for  miles  round,  so  the  jar  pro- 
duced by  the  sudden  cracking  and  slipping  of  a  mass  of  rock  beneath 
it  may  originate  vibrations  which  will  extend  for  long  distances. 

Professor  Milne  remarks  that  "  earthquakes  generally  occur  in 
mountainous  countries  where  the  mountains  are  geologically  young, 
or  in  countries  where  there  is  evidence  of  slow  secular  movements 
like  elevation.  These  latter  movements  are  usually  well  marked  in 
volcanic  countries,  and  it  is  not  unlikely  that  the  majority  of  earth- 
quakes, even  in  volcanic  countries,  are  the  result  of  the  sudden 
yielding  of  rocky  masses  which  have  been  bent  till  they  have 
reached  a  limit  of  elasticity.  The  after-shocks  are  suggestive  of  the 
settling  of  disjointed  strata."* 

It  must  not,  however,  be  forgotten  that  even  very  ancient  moun- 
tain regions,  such  as  the  Scotch  Highlands  or  the  Welsh  hills,  are 
by  no  means,  even  yet,  at  rest,  and  that  volcanic  districts  where  no 
evidence  of  any  marked  flexure  of  the  crust  is  forthcoming  are  not 
seldom  affected  by  rather  long-continued,  if  not  very  severe,  disturb- 
ances. Serious  earthquakes  also,  like  that  of  Charleston,  sometimes 
occur  in  level  districts,  in  which  are  no  signs  of  volcanic  action,  and 
where  a  mountain  range,  if  it  ever  existed,  must  have  been  long 
since  planed  down  by  denudation,  and  must  be  now  buried  deep 
beneath  the  surface.  Still  it  is  probably  true  that  the  more  serious 
shocks  are  due,  as  a  rule,  to  processes  of  mountain  making.  It  is 
impossible  that  such  folding,  crushing,  and  overthrust  faulting,  as 
are  indicated  no  less  plainly  in  the  Highlands  of  Scotland  than  in 
the  mountain  ranges  of  the  Alps,  could  have  occurred  without 
frequent  starts  and  slips,  and  consequent  earth  shudders.  We  are 

*"  British  Association  Reports,"  1892,  p.  128. 


EARTHQUAKES  AND   THEIR  EFFECTS:  283 

prone  to  assume,  often  almost  unconsciously,  that  these  movements 
are  at  an  end,  and  that  no  changes  are  taking  place  in  those  parts  of 
the  earth  where  nature  seems  in  placid  mood  and  we  have  the  good 
fortune  to  live,  but  this  assumption  is  not  supported  by  any  real  evi- 
dence. We  have  seen  that  in  many  regions  the  level  of  the  land 
has  been  very  materially  altered  within  the  last  few  centuries,  some- 
times within  the  last  few  decades.  Hence  we  are  not  entitled  to 
say  more  than  that  in  these  other  districts  no  changes  have  occurred 
which  can  be  readily  perceived.  There  may  be  a  slow  rise  of  the 
surface  here,  a  slow  fall  there,  in  either  the  Highlands  or  the  Alps, 
which  only  a  series  of  very  careful  observations  could  detect,  and  it 
would  be  well  if  even  in  the  British  Isles  a  line  of  levels  were  taken 
from  the  seacoast  across  some  suitable  district  where  earthquakes 
were  frequent  and  good  bench  marks  could  be  made,  and  were  re- 
peated, say,  every  fifty  years,  in  order  to  ascertain  whether  the  sur- 
face of  the  ground  is  perfectly  at  rest. 


CHAPTER  IV. 

INTERNAL   CHANGES   IN   THE   EARTH'S   CRUST. 

THE  uplifting  and  the  downsinking  of  masses  of  land,  the  vol- 
cano and  the  earthquake,  are  but  the  more  obvious  signs  of  proc- 
esses of  change  which  are  ever  at  work  in  the  crust  of  the  earth. 
Into  these,  interesting  though  some  of  them  may  be,  it  is  impossi- 
ble to  enter  fully  in  the  present  volume,  for  the  subject  is  often 
extremely  difficult,  and  a  discussion  of  its  details  cannot  be  made 
intelligible  until  a  considerable  amount  of  rather  minutely  technical 
knowledge  has  been  acquired.  We  must  therefore  be  contented 
with  certain  general  statements  as  to  the  nature  of  these  changes 
and  indications  of  the  more  conspicuous  results  to  which  they  have 
directly  or  indirectly  contributed. 

One  group  of  changes  is  mainly  mechanical,  another  is  mainly 
chemical.  Though  a  hard  and  fast  line  cannot  be  drawn  between 
the  two,  some  advantage  on  the  side  of  simplicity  may  be  found  in 
adopting  this  rough  classification.  A  passing  reference  has  been 
already  made  to  some  of  the  most  striking  phenomena  in  the  former 
group.  By  means  of  the  pressures  set  up  when  masses  of  rock  are 
sharply  folded,  as  happens  in  the  formation  of  a  mountain  chain, 
the  structure  called  cleavage  is  produced,  the  rock  being  traversed 
by  divisonal  planes,  often  very  near  together,  which  are  quite  inde- 
pendent of  and  generally  different  from  those  due  to  the  original 
lamination  of  the  bed.  The  latter  frequently  so  completely  dis- 
appear as  to  be  distinguished  only  by  differences  in  grain  or  in  tint, 
indicating  bands  running  athwart  the  edge  or  across  the  face  of  the 
slab.  That  the  slaty  structure  is  a  result  of  pressure  cannot  be 
doubted  ;  fossils  are  distorted,  and  the  particles  of  the  rock  are 
elongated  parallel  with  the  planes  of  cleavage  ;  the  latter  effect, 
even  if  it  be  not  visible  to  the  naked  eye,  is  always  conspicuous  on 
microscopic  examination.  In  not  a  few  cases  also  the  intimate  rela- 
tion between  the  axes  of  the  folds  which  have  been  formed  in  a 
banded  rock  and  the  direction  of  the  cleavage  planes  proves  that 
both  must  be  the  results  of  the  same  set  of  forces. 

284 


INTERNAL    CHANGES  IN    THE  EARTH'S  CRUST.  285 

By  movements  also  of  the  crust  large  masses  of  rock,  as  already 
mentioned,  have  been  displaced  relatively,  and  faults  have  been 
formed.  Portions  of  rock  which  were  once  in  contact  are  so  no 
longer.  The  displacement  may  be  mainly  in  a  vertical  direction,  or 
also  largely  a  lateral  one  ;  it  may  be  measured  only  by  inches,  or  by 
thousands  of  feet.  In  the  last  case  it  is  most  probable — we  might 
venture  to  say  almost  certainly — the  result  of  a  series  .of  move- 
ments, continued,  doubtless,  with  intervals  of  repose,  through  long 
periods.  A  fault  may  be  often  traced  through  rocks  differing  widely 
in  geological  age,  and  the  displacement  in  the  newer  series  will  be 
much  smaller  than  that  in  trie  older  one.  Hence  it  is  evident  that, 
during  the  interval  between  the  formation  of  the  two  rock  masses, 
the  latter  was  disturbed  and  displaced.  Its  surface  was  subsequently 
planed  down  by  denudation,  and  on  this  comparatively  level  floor  a 
new  set  of  beds  was  deposited.  Then  the  whole  mass  was  subjected 
to  a  strain  acting  in  the  old  direction  ;  the  original  fault  had  pro- 
duced a  line  of  weakness  in  the  crust,  along  which  it  again  yielded, 
so  that  both  sets  of  beds  were  affected,  but  the  newer  bear  record 
of  one  displacement  only,  while  the  older  have  been  twice  moved. 
Faults  sometimes  produce  marked  effects  on  the  scenery  of  a  region. 
As  they  may  bring,  when  the  displacement  is  considerable,  masses 
of  rock  into  contact  which  differ  very  much  in  hardness  and  dura- 
bility, they  may  determine  the  direction  of  valleys  and  the  trend  of 
escarpments ;  but  in  many  instances  they  so  little  modify  the  sur- 
face as  to  be  only  detected  on  a  close  and  careful  examination.  In 
such  cases  the  geologist  infers  their  existence  either  by  finding 
masses  of  rock  outcropping  in  apparent  sequence,  which  from  his 
previous  studies  he  knows  to  be  really  separated  by  considerable 
intervals — that  is  to  say,  by  the  unexpected  disappearance,  as  it 
seems,  of  pages  or  chapters  from  the  geological  record,  or  by  the 
peculiar  and  abnormal  outlines  assumed  by  the  boundaries  of  certain 
deposits,  when  they  are  plotted  down  upon  his  map.  'In  regions 
comparatively  level  the  newer  rocks  as  a  rule  are  simply  dropped 
down,  more  or  less  vertically,  in  comparison  with  the  older  strata. 
Sometimes  a  wedge-like  mass,  between  a  pair  of  faults,  is  let  down, 
as  a  keystone  might  slip  when  an  arch  is  strained  outward  ;  some- 
times, by  a  series  of  parallel  faults,  slice  after  slice  is  dropped,  like 
a  set  of  steps,  each  one  being  displaced  more  than  the  last  (Fig.  90). 
Occasionally  the  fault  has  been  a  gaping  fissure,  which  is  now  filled 
up  by  fragments  and  shattered  (ttbris—a.  fault  breccia,  as  it  is  called 
— separating  the  two  comparatively  unbroken  masses,  but  its  walls 


286  THE   STORY  Of  OUR  PLANET. 

are  often  in  contact,  and  a  peculiar  grooving  and  polishing  of  the 
surfaces  indicates  that  the  one  has  slipped  and  slid  over  the  other.* 

Faults,  of  course,  as  a  rule  are  more  frequent  and  on  a  larger  scale 
among  the  older  strata,  although  a  mass  of  rock  of  one  of  the  later 
geological  ages  may  be  comparatively  undisturbed  in  one  country 
while  it  has  been  greatly  displaced  in  another.  In  England  the 
strata  later  than  the  Chalk  are  but  slightly  affected  by  subsequent 
disturbances.  In  these  the  greatest  dislocation  probably  does  not 
measure  more  than  about  a  hundred  feet  vertical,  and  is  commonly 
much  less,  while  in  the  Alps  beds  of  the  same  geological  age  have 
been  uplifted  to  form  mountain  peaks,  and  have  been  broken  and 
displaced,  during  this  process,  for  thousands  of  feet.  But  among  the 
older  rocks  of  England  the  "  throw  "  f  of  some  of  the  faults  is  very 
large.  By  the  Pennine  fault,  the  western  escarpment  of  the  lime- 
stone hills,  overlooking  the  Vale  of  Eden,  is  largely  defined  ;  its 
throw  amounts  in  places  to  some  3000  feet,  and  that  of  a  fault 
which  occurs  in  the  district  near  Sedbergh  is  estimated  as  hardly 
less  than  5000  feet.  But  dislocations  on  a  yet  grander  scale  may 
be  found  in  America.  A  fault  in  the  Appalachians,  though  it  pro- 
duces no  marked  effect  on  the  scenery,  has  so  dislocated  the  rocks 
that,  in  the  words  of  an  observer,  "  on  one  side  of  a  crack,  over 
which  a  man  can  stride,  the  highest  of  Upper  Silurian  beds  faces  the 
lowest  of  Lower  Silurian.  But  the  Upper  Silurian  wall  of  this  vast 
crack  was  '  denuded,'  hewn  away,  and  the  place  where  it  rose  has 
been  planed  smooth,  so  that  masses  of  grit,  caught  in  the  chinks 
while  it  was  open,  are  cut  through  by  the  surface."  This,  according 
to  the  author  quoted,^:  means  a  displacement  of  some  20,000  feet; 
but  the  process,  no  doubt,  was  gradual,  and  the  surface  all  the  time 
may  have  been  kept,  by  continuous  denudation,  nearly  at  one  level. 

Some  mention  of  joints  has  already  been  made.  These  are  divi- 
sional surfaces  produced  by  a  very  slight  separation  of  rock  masses, 
which,  however,  as  has  been  said,  are  of  great  importance  in  deter- 
mining the  processes  of  denudation,  and  the  outlines  dominant  in 
scenery,  and  sometimes,  as  planes  of  weakness,  may  facilitate  the 


*  This  structure  is  called  (from  a  miner's  name)  slickensides  ;  the  surface  commonly 
appears  as  if  covered  with  a  glaze  ;  sometimes  it  may  be  seen  on  the  faces  of  joints,  espe- 
cially if  they  are  numerous  or  irregular,  and  no  doubt  results  from  oft-repeated  slight 
movements,  such,  for  example,  as  the  tremors  of  earthquakes. 

f  The  term  applied  to  the  amount  of  displacement  estimated  in  a  vertical  direction, 
that  in  a  lateral  direction  being  called  a  "  shift." 

\  Campbell,  "  Frost  and  Fire,"  ch.  li. 


INTERNAL    CHANGES  IN  THE  EARTH'S   CRUST. 


287 


FIG.  115. 

SPHEROIDS  INSIDE  A 
COLUMN,  SHOWING 
INDEPENDENCE  OK 
THESE  AND  THE 

SIDES  (AUVERGNE). 


formation  of  faults,  whether  in  sedimentary  or  in  igneous  rocks.  They 

may  be  attributed  in  both  to  one  cause — contraction  ;  in  the  former 

the  shrinking  is  probably  due  to  the  loss  of  water  in  drying ;  in  the 

latter  to  the  loss  of  heat  in  cooling.     The  cracks 

which  are  formed  in  the  muddy  bed  of  a  pond 

as   the    water   evaporates  are    produced    by   the 

same  cause  as  the  great  divisional  planes  which, 

in  the  Southeastern  Tyrol,  have  denned  the  huge 

towers  of  the  Drei  Zinnen  and  of  Monte  Cristallo. 

The  prismatic  fissures  in  the  sandstone  lining  a 

blast   furnace  have   an  origin  similar   to  that  of 

the  columns  in  Fingal's  Cave,  in  Staff  a,  or  of  the 

Giant's  Causeway,  in  Antrim.     The  regularity  of 

these  prismatic  joints  indicates  the  uniformity  of 

the  strain  to  which  the  mass  has  been  subjected  ; 

that   they   are    very   commonly   hexagonal   is   a 

consequence   of  the  principle  of  least  action,  or, 

in   other    words,    that    Nature,  in   producing  an 

effect,  avoids  the  mistake    so    common    among 

fussy    folk,  and    does  not    expend    more    energy 

than  is  necessary.     The  perimeter  of  a  hexagon, 

for  any  given  area,  is   less  than  that  of  a  square,  and  still  less  than 

that  of  an  equilateral  triangle ;    so  that  when  a  six-sided  prism  is 

formed,  the  materials  in  parting  offer  the  least  resistance.  In  this 

figure  also  the  greatest  amount  of  a 
force  acting  toward  its  center  is 
effective  in  producing  rupture.  It 
follows,  from  both  these  reasons, 
that  when  a  mass  is  submitted  to  a 
uniform  strain  the  cracks  are  likely 
to  assume  a  hexagonal  form.  The 
columns  thus  shaped  are, divided  by 
cross  joints,  which  sometimes  are 
curved,  or  exhibit  a  "  cup  and  ball  " 
structure.  This  is  almost  certainly 
another  consequence  of  contraction, 
which,  by  acting  uniformly  through- 
out a  mass  of  some  thickness,  leads 

to  the  formation  of  cracks  more  or  less  spherical  in  shape.     These 

are  commonest  in  glassy  or  compact  igneous  rocks,  such  as  basalt. 

They  may  be  on  a  very  small  scale,  so  that  the  spheroids  are  hardly 


FIG.  116. 

SPHEROIDAL  STRUCTURE  IN  A  MASS 
OF  VOLCANIC  ASH  (BURNTISI.AND). 


288 


THE   STORY  OF  OUR  PLANET, 


bigger  than  hemp  seeds,  as  in  certain  volcanic  glasses,  or  may  be 
several  inches,  and  even  a  yard  or  so  in  diameter.  Generally  each 
of  these  is  traversed  by  more  than  one  such  divisional  surface,  so  that 
it  consists  of  a  group  of  concentric  shells.  This  structure  is  devel- 
oped by  the  weathering  of  the  rock,  and  thus  the  columns  some- 
times appear  to  be  built  up  of  flattened  balls,  like  Dutch  cheeses. 
Of  this  the  well-known  "  Kase  Grotte,"  near  Bertrich  Baden,  in  the 
Eifel,  is  an  excellent  example. 

Another  group  of  changes  is  rather  of  a  chemical  or  physical 


FIG.  117. — CHEESE  GROTTO,  NEAR  BERTRICH  BADEN. 


character ;  these  are  more  or  less  molecular,  and  may  be  sometimes 
carried  so  far  as  to  alter  completely  the  condition  of  a  rock.  This 
is  then  called  metamorphic,  as  already  stated,  because  its  constitu- 
tion— its  form,  in  the  technical  sense  of  that  word — is  no  longer 
what  it  was  originally.  The  three  principal  agents  in  these  changes 
are  water,  pressure,  and  heat — sometimes  one,  sometimes  another, 
taking  the  largest  share  of  the  work ;  but  where  the  alteration  in 
structure  and  composition  has  been  great,  probably  all  have  played 
a  part,  though  not  necessarily  an  equal  part.  Water,  as  already 


INTERNAL    CHANGES  IN    THE  EARTH'S  CRUST.  289 

described,  is  constantly  at  work,  silently  and  secretly,  in  the  heart  of 
the  rock,  disintegrating  and  dissolving  the  more  soluble  constitu- 
ents, taking  up  from  one  place  to  lay  down  in  another,  and  at  least 
aiding  in  the  formation  of  fresh  mineral  substances.  If  we  examine 
a  thin  slice  of  one  of  the  harder  limestones  with  a  microscope,  we 
see  that  the  fragments  of  various  organisms,  of  which  it  is  largely 
composed,  are  cemented  by  crystalline  carbonate  of  lime.  This 
mineral  must  have  been  deposited  by  the  action  of  water  since  the 
rock  first  was  accumulated,  in  much  the  same  way  as  it  is  precip- 
itated in  the  stalactites  in  the  caves  of  Cheddar,  or  in  the  tufas  at 
the  cascades  of  Tivoli.  Sometimes  also  we  find  that  the  fragments 
themselves  are  beginning  to  undergo  a  change ;  the  structure  char- 
acteristic of  the  organisms  is  beginning  to  disappear,  and  is  being 
replaced  by  that  of  the  mineral.  In  other  cases  the  original  sub- 
stance of  an  organism  has  wholly  vanished,  and  in  its  stead  we  find 
an  exact  model  formed  of  some  other  material.  For  instance,  car- 
bonate of  lime  may  be  converted  into  phosphate  of  lime,  or  it  may 
be  replaced  by  silica,  as  in  the  Greensand  of  Blackdown,  the  flints 
of  the  Chalk,  or  the  cherts  of  the  Derbyshire  limestones.  Some- 
times also,  in  the  case  of  the  last  named,  the  original  organisms 
have  been  first  sealed  up  in  a  mass  of  siliceous  material,  and  have 
been  then  dissolved  away,  so  as  to  leave  an  exact  cast  in  chert  both 
of  their  outer  form  and  of  their  inner  cavities. 

Processes  somewhat  analogous  lead  to  the  concentration  of  par- 
ticular substances  round  fragments,  either  of  minerals  or  of  organ- 
isms, which  play  the  part  of  a  nucleus.  Thus  concretions,  as  they 
are  called,  are  formed.  These  are  sometimes  small,  like  oolitic  or 
pisolitic  structure  (usually  restricted  to  calcareous  rocks),  in  which 
little  balls  vary  from  the  size  of  the  eggs  in  the  "  hardroe  "  of  a  her- 
ring to  that  of  a  pea ;  but  they  are  sometimes  large,  and  the  longest 
diameter  may  occasionally  exceed  a  yard.  They  are  frequently 
about  the  size  of  an  apple,  or  of  a  potato,  often  being  smooth  ex- 
ternally, and  elliptical  in  form,  so  that  one  of  them  might  be  mis- 
taken, at  a  hasty  glance,  for  a  pebble.  Instances  of  such  concretions 
are  afforded  by  the  "  cement  stones,"  common  in  shales  and  clays  of 
different  geological  ages,  which,  on  being  broken  open,  are  generally 
found  to  contain  a  fossil ;  by  the  globular  concretions,  also  calca- 
reous, in  the  Magnesian  Limestones  of  Durham ;  and  by  the  "  penny 
stones,"  or  nodules  rich  in  carbonate  of  iron,  which  are  found  in  the 
clays  among  the  Coal  Measures.  In  the  last  also  a  fossil  usually 
forms  the  nucleus,  as  well  as  in  the  so-called  coprolites. 


290  THE    STORY  OF   OUR   PLANET. 

These  are  all  examples  of  mineral  concentration,  resulting  often 
from  chemical  action  which  is  initiated  by  the  decomposition  of 
organic  substances,  and  is  continued  in  accordance  with  the  principle 
that  in  Nature  "  like  seeks  like."  It  is  a  consequence  of  the  action 
of  water;  it  is  accelerated  by  a  rise  in  temperature;  it  is  indirectly 
facilitated  by  the  action  of  pressure,  which  increases  the  solvent  and 
destructive  power  of  the  fluid,  and  thus,  by  taking  one  mineral  to 
pieces,  prepares  the  way  for  the  formation  of  another. 

But  pressure  alone,  and  heat  alone,  also  bring  about  the  alteration 
of  rocks.  The  one  agent,  though  producing,  as  has  been  shown, 
planes  of  division,  promotes  a  molecular  union  and  consolidates 
the  intervening  particles.  Of  this  experimental  demonstration  can 
be  given  in  certain  cases;  by  heavy  pressure  metals  can  be  welded, 
powdered  graphite  or  "  blacklead  "  can  be  squeezed  into  solid  blocks  ; 
and  by  a  pressure  of  some  950  hundredweight  to  the  square  inch, 
peat  can  be  converted  into  a  substance  resembling  coal.  The  other 
agent,  heat,  ultimately  melts  the  materials  of  rocks,  but  it  also  pro- 
duces considerable  mineral  changes  at  temperatures  below  that  of 
fusion.  The  first  stage  is  that  of  simple  induration,  as  in  the  mak- 
ing of  bricks  and  the  baking  of  pottery  ;  but  at  higher  temperatures, 
or  with  suitable  constituents,  more  marked  mineral  changes  begin. 
One  of  the  most  conspicuous  is  afforded  by  pieces  of  glass  which 
have  been  raised  to  a  high  temperature — perhaps  just  sufficient  to 
soften  them  without  actual  melting.  After  slow  cooling  the  glass 
is  found  to  have  become  an  opaque  white  substance,  consisting  of 
small  needle-like  crystals  thickly  crowded  together,  the  grouping  of 
which  often  appears  to  have  been  influenced  by  the  bounding  sur- 
faces. Glass  may  be  also  affected  in  a  similar  way  by  exposing  it 
to  the  combined  actions  of  heat,  pressure,  and  water.  Professor 
Daubr£e  placed  a  piece  of  it  in  a  strong  iron  vessel  full  of  water, 
which  was  then  securely  closed,  and  subjected  for  several  days  to 
the  heat  of  a  furnace.  On  examination  some  of  the  glass  was  found 
to  have  been  dissolved,  and  small  crystals  of  minerals  formed  from 
it  were  lying  loose  in  the  water ;  the  remainder  was  crowded  with 
small  crystallized  minerals,  as  in  the  case  of  devitrification  already 
described.  The  effect  of  heat  in  the  presence  of  water,  and  under 
a  certain  amount  of  pressure,  may  be  often  studied  in  the  neighbor- 
hood of  intrusive  igneous  rocks.  Small  masses  produce  but  slight 
effects  on  the  sedimentary  materials  ;  sandstones  are  hardened,  lime- 
stones seem  slightly  more  compact,  clays  are  converted  into  a  kind 
of  natural  brick  or  porcelain.  But  large  masses,  especially  of 


INTERNAL    CHANGES  IN   THE  EARTH'S  CRUST.  291 

granite,*  produce  changes  which  may  be  traced  for  some  hundreds 
of  yards.  As  we  proceed  toward  the  intruder,  the  limestones 
gradually  become  coarsely  crystalline,  all  traces  of  fossils  disappear- 
ing, and  new  minerals  are  developed,  the  latter  coming  from  a 
slight  amount  of  muddy  sediment  which  is  present  in  all  but  the 
very  purest  limestones.  But  the  change  is  most  marked  in  clayey 
rocks,  such  as  shales  or  slates.  In  these  various  aluminous  silicates 
are  formed,  one  of  the  most  characteristic  being  a  peculiar  brown 
mica.  These  minerals,  at  first  small  and  ill  defined,  become  larger 
and  better  developed  as  the  intruding  mass  is  approached.  More- 
over, granules  of  quartz,  if  originally  present,  are  enlarged,  and  new 
grains  are  formed  ;  at  last  the  rock  loses  all  resemblance  to  a  sedi- 
ment, and  becomes  a  crystallized  mass,  hard  and  solid. 

But  in  rocks  of  a  suitable  character  many  changes  are  probably 
due  to  the  action  of  water  and  pressure,  with  little,  if  any,  rise  of 
temperature.  Among  these  may  be  included  a  kind  of  devitrifica- 
tion frequently  occurring  in  certain  ancient  lavas  which  are  believed 
(with  good  reason)  to  have  been  formerly  glassy,  and  the  conversion 
of  rocks  which  once  consisted  mainly  of  olivine  into  the  material 
called  serpentine,  so  largely  employed  for  ornamental  purposes. 
In  the  last  case  the  change  is  one  of  hydration — that  is,  caused  by 
the  entry  of  water  into  chemical  combination  with  certain  of  the 
constituents. 

A  rock  is  called  metamorphic  when  these  changes  have  been 
carried  so  far  that  its  original  character  is  ascertained  with  great 
difficulty.  Many  such  rocks  exhibit  a  peculiar  structure  called 
foliation.  This  term  implies  a  distinct  tendency  to  a  parallelism  in 
one  or  more  of  the  mineral  constituents.  All  such  rocks  are  obvi- 
ously crystalline,  and  to  them  alone  the  name  schist  is  properly 
applied.  In  some  cases  not  only  is  this  structure  exhibited,  but 
also  certain  of  the  component  minerals  are  more  or  less  aggregated 
so  as  to  form  bands.  The  origin  of  the  crystalline  schists,  with 
which  the  gneisses  may  be  included,  is  a  very  difficult  question, 
which  has  been  the  subject  of  many  controversies.  That  not  a  few 
schists  were  orginally  sediments,  and  have  been  subsequently  altered, 
may  be  regarded  as  certain.  The  mud  has  become  a  mica-schist, 
the  limestone  a  marble  or  a  calc-schist,  the  sandstone  a  quartzite  or 
a  quartz-schist ;  but  there  are  other  schists,  the  origin  of  which 

*  It  must  be  remembered  that  when  an  igneous  rock  is  coarsely  crystalline,  this  is  an  in- 
dication of  its  having  cooled  slowly,  and  at  a  considerable  depth  from  the  surface — i.  <?., 
under  a  fair  amount  of  pressure. 


292  THE   STORY  OF  OUR  PLANET. 

must  have  been  different.  A  foliated  structure  may  result  from  the 
crushing  of  an  igneous  rock,  which  has  been  followed  by  a  certain 
amount  of  mineral  reconstitution.*  This  seems  to  take  place  in 
rocks  already  crystalline,  more  readily  than  in  ordinary  sediments. 
In  this  way  certain  gneisses  and  schists  have  been  produced.  Other 
rocks  may  have  been  foliated  from  the  very  first,  and  the  structure 
may  be  the  result  of  slow  movements  as  the  mass  gradually  became 
cool  and  solidified.f 

Mineral  veins  may  be  mentioned  in  connection  with  this  subject. 
An  explanation  of  their  history  involves  many  difficulties,  and  can- 
not receive  detailed  treatment  in  a  work  such  as  this.  So  since, 
notwithstanding  their  great  commercial  importance,  they  affect  but 
small  portions  of  the  earth's  crust,  they  must  receive  only  a  passing 
notice.  A  mineral  vein  appears  generally  to  have  originated  in  a 
fissure.  This  has  been  sealed  up,  more  or  less  completely,  by  a  mass 
of  minerals,  which  sometimes,  as  it  were,  impregnate  the  adjacent 
rock.  The  veins  may  contain  few  or  several  minerals,  one  or  more 
of  these  commonly  being  a  metal  or  a  metallic  ore,  but  no  hard 
and  fast  line  can  be  drawn  between  a  metalliferous  and  any  other 
vein.  The  minerals  appear  to  have  been  deposited  by  water, 
and  sometimes  to  have  been  derived  from  the  neighboring  rock, 
sometimes  to  have  been  brought  from  below.  It  may  be 
inferred  that  the  latter  is  of  frequent  occurrence  from  the  mode 
in  which  the  adjacent  rock  is  affected  and  impregnated.^:  In  many 
cases  the  water  probably  was  at  a  high  temperature.  For  instance, 
at  Steamboat  Springs,  Nev.,  and  Sulphur  Bank,  Cal.,  §  fissures 
are  now  ejecting  steam  or  hot  water,  and  are  being  gradually 
filled  with  silica  (first  colloid,  then  crystalline)  and  various  other 
minerals,  among  them  sulphides  of  iron  and  of  mercury,  and  even 
gold.  Thus  the  formation  of  a  mineral  vein  often  indicates  a  stage, 
generally  an  expiring  one,  in  volcanic  action.  They  are  striking 
illustrations  of  the  changes  which  can  be  wrought  in  rocks  by  the 
action  of  subterranean  water  at  a  high  temperature.  || 

*  There  is  no  proof  that  a  banded  structure  can  be  produced  in  this  way. 

f  This  case  is  analogous  to  the  formation  of  the  streaky  structure  seen  in  certain  slags 
and  vitreous  lavas. 

\  The  nature  of  the  rock  appears  sometimes  to  have  an  effect  on  the  mineral  deposited, 
for  it  is  noticed  that  if  a  fissure  traverses  two  kinds  t>f  rock  there  is  a  corresponding  change 
in  the  ore  ;  differences  also  in  the  temperature  of  the  water  will  determine  the  order  in 
which  it  deposits  particular  substances. 

§  A.  Phillips,  Quarterly  Journal  of  the  Geological  Society,  vol.  xxxv.  1879,  P-  39°- 

|  See  the  notice  of  mineral  springs,  p.  117. 


INTERNAL   CHANGES  IN    THE  EARTH'S  CRUST.  293 

Thus,  by  a  variety  of  processes,  mechanical  movements  and  mo- 
lecular changes  have  produced  effects  in  the  crust  of  the  earth,  as  far 
down  at  least  as  man  has  been  able  to  submit  any  part  of  it  to 
examination.  To  what  depth  they  may  be  continued  he  has  no 
means  of  ascertaining.  Wherever  air  or  water  can  penetrate,  there 
chemical  change  is  almost  certain  to  occur,  there  the  antagonistic 
but  compensatory  processes  of  disintegration  and  of  combination 
are  sure  to  carry  on  their  task  of  destroying  and  of  building.  They 
began  it  when  this  planet  first  gathered  into  solid  form,  as 

Ilion  like  a  mist  rose  into  towers  ; 

they  will  continue  it  till  that  far-off  day  when,  in  consequence  of  the 
dissipation  of  energy,  "  the  sun  itself  shall  die,"  and  the  earth,  airless 
and  waterless,  shall  be  rigid  in  the  cold  of  outer  space. 


PART  IV. 
THE  STORY  OF  PAST  AGES. 


CHAPTER  I. 

METEORS  AND  THE   EARTH'S  BEGINNING. 

IN  the  preceding  chapters  an  outline  is  given  of  the  processes 
which  obviously  are  still  at  work  in  changing  the  surface  of  our 
planet  and  in  modifying  the  structure  of  its  crust.  It  has  been  our 
endeavor  to  describe  and  make  clear,  as  far  as  our  limits  permitted, 
the  facts  which,  on  an  inductive  study,  establish  those  principles  of 
geology  in  accordance  with  which  the  earth's  present  contours  and 
the  existing  distribution  of  land  and  water  are  explained,  and  its 
physical  geography  in  past  epochs  is  inferred  from  the  testimony 
of  the  rocks  themselves.  Remote  as  these  epochs  may  be,  imper- 
fect as  their  record  too  often  is,  we  may  confidently  reason  as  to 
the  significance  and  interpretation  of  their  character  in  reliance  on 
the  general  uniformity  of  Nature's  operations — viz.,  that  similar 
effects  are  the  results  of  similar  causes  ;  or,  in  other  words,  that  the 
marks  which  at  the  present  time  denote  the  action  of  the  stream, 
the  wave,  or  the  glacier,  are  indicative  of  the  same  forces  in  every 
age  of  the  globe,  and  that  the  structure  which  now  characterizes 
a  particular  group  of  organisms  is  a  proof  that  a  similar  group  was 
in  existence,  at  the  geological  epoch,  in  the  rocks  of  which  this 
structure  has  been  detected.  If  a  pebble  of  a  certain  shape  and 
weight  is  now  moved  by  a  current  of  a  known  velocity,  if  fragments 
of  a  certain  kind  are  now  ejected  and  accumulated  by  volcanic 
explosions,  if  some  structures  are  characteristic  of  rocks  which  have 
been  deposited  by  water,  and  others  of  rocks  which  have  become 
solid  from  a  state  of  fusion — if,  for  example,  no  hardened  sediment 
bears  any  real  resemblance  to  a  basalt,  and  no  limestone  could  pos- 
sibly be  ejected  as  a  stream  of  lava  from  a  volcano — we  have  no 
hesitation  in  asserting  that  the  same  conclusions  must  hold  good  in 
any  geological  epoch,  so  long  as  the  conditions  on  this  planet  were 
practically  identical  with  those  which  still  exist.  It  is  probable, 
indeed,  that  as  we  retrace  the  history  of  the  globe  these  conditions 
will  gradually  become  less  like  those  which  still  prevail,  but  the 
variation  even  then  will  be  in  degree  rather  than  in  kind.  The 


298  THE   STORY  OF  OUR  PLANET. 

changes  will  still  be  gradual  in  the  main,  even  if  they  be  quicker 
than  at  present ;  they  will  be  of  like  nature,  in  all  probability,  so 
long  as  the  earth  may  be  regarded  as  a  solid  body,  and  certainly 
during  all  the  time  since  it  has  become  fit  to  be  inhabited  by  living 
creatures.  Toward  the  beginning  of  this  period  we  must  walk 
warily,  even  in  following  the  inductive  path  ;  and  in  regard  to  that 
which  was  anterior  to  it  we  must  argue  from  analogy,  and  so  must 
venture  cautiously  on  hypothesis.  In  preparing  to  deal  with  this 
far-off  epoch  the  geologist  must  lift  his  eyes  from  the  ground 
beneath  his  feet,  and  look  upward  to  the  orbs  of  heaven  and  the 
star-studded  region  of  the  sky.  He  must  be  content  to  seek  help 
from  the  student  of  physics  and  the  astronomer. 

We  shall  endeavor  in  the  following  chapters  to  tell,  in  its  broad 
outlines,  the  story  of  the  earth,  and  to  indicate  the  steps — if  such 
a  term  be  permissible — by  which  it  was  prepared  to  be  the  scene  of 
the  drama  of  man's  life.  "  All  the  world's  a  stage,"  but  this  par- 
ticular theater  has  been  long  in  building.  The  tragedy  or  the 
comedy  of  human  life  is  in  itself  only  a  denouement  up  to  which  the 
ages  of  the  past  have  been  gradually  leading.  We  might  tell  the 
tale,  as  geologists  have  deciphered  its  record,  by  working  back 
from  the  present  to  the  past,  but  the  usual  historical  method  is  far 
preferable.  "  In  the  beginning  "  is  a  natural  opening  for  every 
story,  and  we  shall  endeavor,  in  this  rough  sketch,  to  trace  our 
planet's  course  along  the  corridors  of  time,  and  to  commence  in 
that  dim  and  distant  epoch  when  it  might  be  said,  in  the  words 
where  poetry  joins  hands  with  science,  that  "  the  earth  was  without 
form  and  void." 

By  day  the  sun  warms  and  illuminates  this  planet,  by  night  the 
clear  sky  is  studded  thick  with  "  patines  of  bright  gold  "  ;  these, 
too,  are  suns ;  these  may  be  each  one  the  center  of  a  planetary 
system.  Across  the  "  black  concave,"  like  drops  of  condensed 
light,  the  "  shooting  stars,"  as  they  are  poetically  called  by  simple 
folk,  the  meteors,  as  they  are  named  in  the  tongue  of  science,  dart 
or  glide  through  the  darkness.  At  intervals  more  rare  the  comet 
gleams  like  a  pale  torch  among  the  brighter  sparkles,  and  the 
nebulae  seem  as  clouds  faintly  luminous  in  the  awful  darkness  of 
outer  space.  Comets,  nebulae,  meteors,  suns — what  light  can  they 
throw  on  that  beginning  of  which  man  inquires  hardly  less  curiously 
than  of  the  end  which  he  tries  to  forecast  for  himself,  his  race,  and 
the  world?  Whence  and  whither? — that  is  the  question  which 
some  occult  impulse  drives  us  all  to  ask  of  our  environment.  To 


METEORS  AND   THE  EARTtfS  BEGINNING.  299 

the  latter  clause  science  cannot  reply,  to  the  former  it  can  return 
only  a  halting  and  uncertain  answer ;  but,  since  "  the  oracles  are 
dumb,"  if  this  fail  to  satisfy  us,  we  shall  find  no  other  response. 

With  such  meteors  as  fall  upon  the  earth  the  chemist  and  mineral- 
ogist has  no  more  difficulty  in  dealing  than  with  any  other  rock 
fragment.  He  finds  them  to  be  masses,  more  or  less  crystalline,  of 
minerals  already  well  known  by  his  researches  among  terrestrial  sub- 
stances. The  great  majority  consist  mainly  either  of  pure  iron  or 
of  some  admixture  of  this  with  ferro-magnesian  silicates,  among 
which  the  mineral  olivine  is  the  most  abundant.  With  these  small 
quantities  of  other  well-known  elements  are  present,  as,  for  example, 
chromium,  nickel,  aluminium,  calcium,  and  carbon.*  All  these  occur 
in  terrestrial  bodies;  from  the  study  of  meteorites  no  new  element 
has  been  obtained.  Iron,  which  is  so  abundant  in  them,  is  a  metal 
with  which  we  are  all  familiar;  it  is  present,  occasionally  in  con- 
siderable quantity,  in  almost  every  igneous  rock,  and  some  geolo- 
gists are  of  opinion  that  certain  dyke-like  masses  of  its  oxide  have 
had  an  eruptive  origin.  Those  meteors  which  consist  chiefly  of  oli- 
vine correspond  precisely  with  a  well-known  rock,  certainly  igneous, 
called  peridotite;f  this  rock,  it  is  interesting  to  note,  has  been 
hardly  ever  ejected  as  scoria,  perhaps  has  never  formed  a  lava  flow. 
It  appears  to  represent  some  rather  deep-seated  material.  Native 
iron  also,  though  it  has  been  discovered  in  lava  (basaltic),  sometimes 
in  masses  of  considerable  size,  generally  occurs  in  such  cases  as  lumps, 
which  seem  as  if  they  had  been  caught  up  and  transported  by  the 
rock  in  which  they  have  been  discovered. 

The  meteorites,  then,  consist  of  the  same  materials  as  the  earth's 
crust,  and  may  be  regarded  as  samples  which  are  representative  of 
its  more  deep-seated,  rather  than  of  its  most  superficial,  portion. 
But  these  meteorites  appear  to  abound  throughout  all  that  portion 
of  space  which  is  traversed  by  our  globe.  Besides  the  two  great 
"swarms"  which,  as  astronomers  now  believe,  circle  about  the  sun 
in  huge  elliptical  orbits,  one  of  which  is  traversed  by  the  earth 
about  the  middle  of  August,  and  the  other  early  in  November, 
scarce  a  night  passes  without  some  solitary  travelers  from  this  un- 
numbered horde  of  celestial  vagrants  crossing  the  track  of  the 
earth.  Moving  in  obedience  to  the  same  laws  as  our  planet,  though 
we  know  not  in  what  orbits,  they  dash  through  its  atmosphere  at  a 

*This  has  been  found  crystallized  in  two  forms,  the  most  recently  discovered  in  meteors 
being  the  diamond. 

f  This,  as  already  said,  is  more  commonly  met  with  in  its  altered  form,  "  serpentine." 


300  THE   STORY  OF  OUR  PLANET. 

rate  which  "  is  perhaps  one  hundred  times  that  of  a  rifle  bullet." 
Previous  to  that  they  had  circled  in  the  emptiness  of  space  "  for 
thousands,  perhaps  millions,  of  years  without  let  or  hindrance,  but 
the  supreme  moment  arrives,  and  the  meteor  perishes  in  a  streak  of 
splendor."  By  friction  with  air  they  are  intensely  heated,  raised  to 
a  temperature  so  high  that  they  glow  with  incandescent  light  as  they 
dart  across  the  sky;  sometimes  they  are  dissipated  into  glowing 
dust  or  luminous  vapor,  which  marks  for  a  few  moments  their  path 
through  the  atmosphere  before  the  darkness  once  more  swallows  it 
up ;  sometimes  they  vanish  again  into  space,  deflected  into  a  new 
path,  and  are  no  more  seen ;  sometimes  they  are  caught  by  the 
attraction  of  the  huge  mass  of  the  earth  and  fall  upon  its  surface. 
There  is  no  reason  to  suppose  that  these  migratory  flights  of 
meteors  are  restricted  just  to  that  portion  of  space  in  which  the 
earth  performs  its  annual  journey  ;  the  whole  solar  system  may  well 
be  permeated  with  this  dust  of  worlds.  Many  astronomers  believe 
that  meteors  are  showering  down  upon  the  sun  in  a  constant  and 
increasing  hail,  and  maintain,  like  fuel,  the  light  and  heat  of  the 
central  orb.  If  this  be  so,  and  it  is  probably  true,  we  might  have 
argued,  that  since  the  center  of  our  system  is  not  stationary,  but  the 
sun  itself  is  ever  speeding  onward,  space  also  should  be  similarly 
filled.  But  without  entering  upon  this  wide  question,  even  if  we 
consider  the  meteors  of  which  we  have  cognizance  to  be  denizens  of 
our  own  system,  we  are  justified  in  regarding  them  as  "  chips  from 
Nature's  workshop,"  and,  as  such,  indicative  that  the  materials  which 
have  been  employed  in  the  making  of  worlds  are  not  unfairly  repre- 
sented in  our  own — in  other  words,  that  any  hints  which  may  be 
supplied  by  the  study  of  the  members  of  the  solar  system  may  be 
utilized  in  explaining  the  composition  and  history  of  our  own  globe. 
If  we  read  the  story  of  the  sun,  we  shall  find  in  it  many  facts 
which  strongly  support  this  inference,  and  are  illustrations  of  the 
probable  constitution  of  the  earth.  The  sun,  as  astronomers  are 
now  generally  agreed,  consists  of  a  huge  mass  of  matter,  sur- 
rounded by  a  luminous  atmosphere.  The  inner  mass  is  at  a  high 
temperature,  but  the  outer  zone  is  so  much  hotter,  is  quivering 
with  vibrations  so  intense,  that  the  inner  orb  seems  dark  in  com- 
parison with  it,  and  chemical  combination  between  its  constituent 
elements  is  impossible.  The  sun,  as  a  whole,  "  is  infinitely  hotter 
than  a  Bessemer  converter  or  a  Siemens  furnace."  Of  late  years 
several  skillful  observers  have  undertaken  comparative  studies  of 
the  spectra  of  telluric  elements  and  of  the  sun.  Perhaps  the  latest 


METEORS  AND  THE  EARTH'S  BEGINNING.  301 

and  most  complete  are  those  by  Professor  H.  A.  Rowland,  the 
result  of  whose  researches  may  be  thus  briefly  summarized : 
"  Practically  all  the  known  elements,  with  the  exception  of  a  few 
very  rare  ones,  and  one  or  two  gases,  have  been  compared  with  the 
solar  spectrum.  .  .  Some  thirty-six  elements  have  thus  been 
identified  in  the  sun,  the  cases  of  eight  more  are  considered  doubt- 
ful, and  fifteen  are  not  represented  in  the  solar  spectrum.  Of  the 
last  class  Professor  Rowland  points  out  that  most  of  them  have 


FIG.  118. — SURFACE  OF  THE  SUN,  AS  SHOWN  BY  A  SOLAR  SPOT. 

few,  if  any,  strong  lines  within  the  limit  of  the  solar  spectrum, 
when  the  arc  spectrum,  which  he  employed,  is  used.  Some  good 
reason,  he  adds,  generally  appears  for  their  absence  from  the  solar 
spectrum.  Of  course  there  is  little  evidence  of  their  absence  from 
the  sun  itself ;  were  the  whole  earth  heated  to  the  temperature  of 
the  sun,  its  spectrum  would  probably  resemble  that  of  the  sun  very 
closely."  *  We  learn,  then,  from  students  of  solar  physics  that  in 
this  huge  mass  materials  similar  to  those  of  the  earth  are  collected, 
though  not  necessarily  in  the  same  proportion,  only  in  it  they  are 
glowing  with  an  intense  heat,  which,  at  any  rate  in  the  visible  part, 
is  so  great  as  to  prevent  chemical  combination — heat  which  sur- 

*  Professor  Rowland,  "Johns  Hopkins  University  Circular,"  No.  85,   from  summary  in 
"  Yearbook  of  Science  "  for  1891. 


3^2  THE   STORY  Of  OUR  PLANET. 

passes  even  that  of  fused  platinum,  and  perhaps  the  highest  temper- 
ature obtainable  in  our  laboratories. 

From  the  sun,  the  center  of  this  system,  astronomers  have  turned 
their  spectroscopes  upon  the  stars — bodies,  certainly,  no  less  vast — 
some  of  which,  as  it  has  been  discovered,  burst  forth  at  times  into 
a  brighter  blaze.  In  the  results  obtained  by  their  researches  differ- 
ences have  been  observed  which  have  been  used  for  purposes  of 
classification.  In  the  first  group  of  these  far-off  suns  are  placed 
intensely  white  stars,  like  Sirius  and  Vega/  Comparatively  few 
lines  are  exhibited  by  their  spectra,  but  those  of  hydrogen  are  very 
strong,  so  this  gas  evidently  forms  a  large  part  of  their  atmospheres, 
as  in  that  of  our  sun ;  the  lines  of  calcium  and  magnesium  also  have 
been  detected,  but  they  are  faint.  The  spectra  of  the  second  group 
of  stars  closely  resemble  that  of  the  sun.  "  The  chief  hydrogen  lines 
are  conspicuous,  but  many  metallic  lines  are  coming  strongly 
out."*  The  third  type  exhibits  many  metallic  lines,  but  hydrogen 
is  absent.  This  evidence,  so  far  as  it  goes,  indicates  that  even  in 
the  immensity  of  space,  through  which  these  thousand  myriads  of 
suns  are  moving,  doubtless  in  obedience  to  the  same  laws  that 
regulate  our  solar  system,  there  is  a  general  community  of  material. 
But  this  is  not  quite  all.  The  comets,  attenuated  as  is  their  sub- 
stance, inappreciably  slight  as  is  their  mass,  consist  apparently  of 
hydrogen,  with  various  compounds  of  carbon,  possibly  chlorine, 
and  some  other  terrestrial  substances.  The  spectroscope  also  has 
been  turned  on  the  nebulae,  those  clouds  of  glowing  gas  which,  on 
a  clear  night,  gleam  ghostly  in  the  blackness  of  the  star-studded 
sky.  "  It  is  believed  that  some  of  these  are  sunk  in  space  to  such 
an  appalling  distance  that  the  light  takes  centuries  before  it  reaches 
the  earth.  We  see  these  nebulas,  not  as  they  are  now,  but  as  they 
were  centuries  ago."  Yet,  so  far  as  information  at  present  goes,  the 
lines  in  the  spectra  of  these  mysterious  star  clouds  have  revealed 
the  presence  of  familiar  substances,  such  as  hydrogen  and  nitrogen, 
though  there  are  also  some  lines  which  cannot  be  identified  with 
known  elements.  It  is  possible,  of  course,  that  every  elemental 
substance  is  only  a  form  or  mode  of  manifestation  of  some  one 
common  matter,  so  that  in  the  apparent  diversity  of  inorganic 
nature  there  may  be  a  latent  unity.  But  this  is  a  question  which 
lies  outside  our  immediate  purpose,  one  concerning  which  too  little 
is  at  present  known  to  make  it  of  any  practical  value  for  this 

*Sir  R.  S.  Bill,  "  The  Story  of  the  Heavens,"  ch.  xxii. 


METEORS  AND    THE  EARTH'S  BEGINNING.  303 

inquiry.  So  it  follows  as  one  result  of  these  investigations  that 
worlds,  at  any  rate  in  our  solar  system,  are  constructed  of  the  same 
materials,  though  these  are  not  necessarily  aggregated  always  in 
the  same  proportion.  In  some  the  heavier,  in  some  the  lighter, 
substances  may  predominate  ;  elements  may  exist  in  some  which 
are  absent  in  others  ;  in  all  cases  obviously  our  knowledge  only 
extends  to  such  constituents  as  are  present  in  these  bodies  at  a 
temperature  so  high  as  to  be  luminous  enough  to  affect  a  spectro- 
scope, and  it  is  little  more  than  skin  deep  in  the  case  of  the  earth, 


FIG.  119. — THE  ANNULAR  NEBULA  IN  LYRA. 

which  is  our  standard  of  comparison.  But  so  far  as  our  knowledge 
extends,  it  is  very  favorable  to  the  idea  that  sun,  planets,  and 
moons,  in  this  system,  have  had  a  common  origin,  have  been 
developed  from  some  primary  condition  of  a  mass  of  materials 
which  have  gradually  become  what  they  are  at  present.  The  state- 
ment very  likely  might  be  extended  to  all  stellar  space.  We  know 
of  no  reason  why  it  should  not  be  full  of  worlds  and  systems,  in 
various  phases  of  development,  in  every  stage  from  birth  to  death 
— if  such  terms  be  applicable,  from  the  condition  of  a  nebula  to  that 
of  the  satellite  of  this  earth. 

Is  it,  then,  possible  to  speculate,  to  form  any  reasonable  hypothe- 
sis, as  to  the  initial  condition  of  our  earth  and  of  the  solar  system 
to  which  it  belongs  ?  This  has  been  attempted,  and  the  hypothesis 
at  any  rate  has  the  merit  of  comparative  simplicity.  It  may  be 
briefly  stated  as  follows  :  Suppose  a  portion  of  space  to  have  been 
formerly  occupied  by  an  enormous  body  of  matter,  consisting 
mainly  or  wholly  of  gas  at  a  high  temperature — in  other  words,  a 
vast  nebula,  like  that  which  gleams  below  the  Belt  of  Orion.  Sup- 
pose that  this  body,  as  seems  to  be  the  case  with  some  of  the 
nebulae,  were  rotating  about  an  axis.  "  The  hot  mass  will  cool  and 
so  contract.  Contraction  will  make  it  rotate  faster.  You  are  all 


304  THE   STORY  OF  OUR  PLANET. 

familiar  with  the  domestic  experiment  of  twirling  a  mop.  At  first 
no  results  follows,  but  as  you  spin  it  faster  and  faster  the  water  at 
last  begins  to  fly  off.  In  the  same  way  the  nebulous  ball  will  at  last 
spin  at  such  a  rate  that  it  can  no  longer  hold  together,  and  a  ring 
will  be  thrown  off  round  its  equator."  This,  of  course,  will  be  at 
the  end  of  a  gradual  deformation.  If  the  original  mass  were  a 
sphere,  this,  as  the  rate  of  rotation  increased,  would  become  more 
and  more  spheroidal  in  outline,  the  polar  diameter  diminishing  as 
the  equatorial  increased,  until  at  last  the  protuberant  part  became 
separated  from  the  main  mass.  "  The  ring  will  at  first  spin  round 
in  the  same  direction  as  the  ball  it  has  left.  But  the  ring  cannot 
hold  together."  It,  too,  is  losing  heat,  and  then  soon  becomes 
exposed  to  other  strains  than  that  caused  by  its  rotation.  "  It  breaks 
up  and  collects  into  a  ball.  This  ball  revolves  in  the  same  direction 
as  the  nebula  of  which  it  originally  formed  a  part,  and  at  the  same 
time  rotates  in  the  same  direction  around  an  axis  parallel  to  the 
axis  of  rotation  of  the  nebula. 

"  Further  contraction  will  cause  another  ring  to  be  thrown  off, 
which  will  likewise  collect  into  a  ball.  So  in  the  end  we  shall  have 
a  number  of  balls  all  revolving  in  the  same  plane  about  a  common 
center,  and  rotating  all  in  the  same  direction  about  axes  perpendic- 
ular to  that  plane,  and  in  the  center  a  large  mass  still  in  a  gaseous 
and  heated  state.  These  balls,  being  small,  will  cool  and  condense 
into  planets ;  the  central  mass,  being  large,  will  retain  its  heat  much 
longer,  and  will  form  a  sun.  It  may  happen  that  some  of  the  balls 
will,  as  they  contract,  throw  off  rings,  which  will  collect  into  balls, 
and  so  we  shall  get  moons  revolving  about  some  of  the  planets." 

"  This  is  very  nearly  the  constitution  of  our  solar  system.  With 
one,  or  perhaps  a  few,  singular  exceptions  among  the  outermost 
bodies,  the  planets  and  moons  all  move  round  the  sun  in  the  same 
direction  and  in  planes  inclined  to  one  another  at  small  angles,  and 
all  rotate  upon  axes  nearly  perpendicular  to  their  common  plane  of 
revolution  in  the  same  direction  as  they  revolve." 

"  The  probability  that  such  an  arrangement  could  have  been 
brought  about  by  chance  is  so  infinitesimally  small  that  we  are  driven 
to  the  belief  that  it  is  a  necessary  consequence  of  the  way  in  which 
the  solar  system  came  into  existence.  The  facts  point  to  some 
common  origin  for  all  the  members  of  the  system,  and  to  some 
common  scheme,  according  to  which  the  system  was  grown  into  its 
present  shape ;  assuming,  of  course,  that  it  has  reached  its  present 
state  by  some  process  of  natural  evolution,  an  assumption  to  which 


METEORS  AND    THE  EARTH'S  BEGINNING,  305 

analogy  leads.  The  nebular  hypothesis  furnishes  us  with  such  a 
scheme  and  such  an  origin."  * 

This  hypothesis  was  first  stated  explicitly  about  the  middle  of  the 
last  century  by  the  great  German  philosopher  Immanuel  Kant ;  but 
it  was  advanced  independently  and  in  a  more  systematic  and  devel- 
oped form  by  Laplace  shortly  before  the  end  of  the  same  century. 
Additional  probability  was  lent  to  it  by  an  ingenious  experimental 
illustration,  devised  by  a  Belgian  savant,  M.  Plateau.  By  means  of 
a  mechanical  contrivance  he  succeeded  in  imparting  a  rotation  to  a 
ball  of  oil,  as  it  floated  in  a  mixture  of  water  and  spirits  of  wine, 
which  was  of  exactly  the  same  specific  gravity,  and  he  was  able  to 
increase  at  pleasure  the  velocity  of  rotation.  As  this  was  done,  the 
globe  of  oil  gradually  flattened  at  the  poles  and  bulged  at  the 
equator.  Then,  as  it  was  made  to  whirl  round  yet  more  rapidly,  it 
threw  off  a  ring,  which  presently  was  followed  by  another  and 
another.  Each  of  these  in  turn  suddenly  broke  up  and  assumed  the 
form  of  a  little  ball,  rotating  on  its  axis  and  revolving  in  an  orbit 
about  the  central  globe.  Here  obviously  the  fracture  was  due  to 
the  expansion.  The  precise  cause,  no  doubt,  which  brought  about 
the  result  in  Plateau's  expe'riment  was  different  from  that  which  is 
supposed  to  have  occurred  in  Nature.  The  strain  in  the  one  is 
caused  by  increasing  the  velocity  of  rotation,  in  the  other  by  con- 
traction through  loss  of  heat ;  still  the  principle  is  similar,  and 
forces  opposite  in  sign,  as  they  would  be  called  by  mathematicians, 
often  produce  results  which  are  alike  in  kind.  So  close  is  the  gen- 
eral resemblance  presented  by  the  experiment  that  "  anyone  looking 
at  it  might  well  fancy  it  was  an  exact  representation  of  the  solar 
system."  f 

Let  us  follow  rather  further  the  history  of  one  of  these  planetary 
masses  detached  from  the  central  sun.  It  is  composed  of  somewhat 
similar  material,  and  even  at  the  moment  of  severance  probably  is 
still  in  a  more  or  less  nebulous  condition,  and  at  a  very  high  tem- 
perature. As  it  proceeds  on  its  journey  heat  is  lost  by  radiation 
into  space  ;  the  temperature  of  the  whole  mass  falls,  but  the  outer 
layers  are  especially  chilled.  For  a  considerable  while  there  will  be 
an  up  and  down  movement  in  the  orb — the  cooler  matter  descend- 
ing from  the  exterior,  the  hotter  ascending  from  the  interior.  By 


*  The  above  extracts  are  taken  from  Professor  A.   H.  Green's  lucid  and  pleasantly 
written  little  book,  the  "  Birth  and  Growth  of  Worlds,"  p.  42. 
f  Reclus.  "  The  Earth,"  part  i.  ch.  iii. 


306  THE   STORY  OF  OUR  PLANET. 

this  means,  in  process  of  time,  a  kind  of  stratification  will  be  pro- 
duced in  the  mass,  the  lighter  and  more  readily  vaporized  substances 
working  their  way  toward  the  exterior,  the  heavier  and  those  which 
most  readily  solidify  accumulating  at  the  interior.*  This  transfer- 
ence and  selective  ordering  will  continue  so  long  as  the  materials  of 
the  planet  remain  in  a  vaporous  or  even  in  a  thoroughly  liquid  con- 
dition. But  as  time  goes  on  internal  movements  and  relative  dis- 
placements will  become  more  difficult.  The  outer  surface  of  the 
globe  will  begin  to  crust  over,  and  the  condition  of  the  interior — 
whether  simultaneously  or  not  we  cannot  say — will  be  modified  by 
another  cause.  Here,  obviously,  the  condensation  of  the  mass  pro- 
duces a  tremendous  pressure.  The  high  temperature  of  the  interior 
tends  to  drive  its  molecules  apart  one  from  another,  but  the  weight 
of  the  outer  layers  tends  to  pack  them  closer  and  closer,  and  thus  to 
produce  a  solid  nucleus.  The  two  tendencies  are  antagonistic,  and 
our  knowledge  does  not  yet  enable  us  to  determine  which  of  the  two 
will  prevail. 

To  this  point,  however,  we  must  refer  again  in  considering  the  ques- 
tion of  the  probable  condition  of  the  earth's  interior.  It  may  suffice 
for  the  present  to  say  that  some  while  after  the  earth  had  commenced 
its  journey  as  an  independent  planet,  but  perhaps  not  long  after 
its  own  satellite  had  been  detached,  its  outer  part  must  have  been 
gradually  covered  with  a  crust.  Assuming  this  to  have  been  com- 
posed of  such  materials  as  are  now  ejected  from  volcanoes,  it  would 
contract,  though  perhaps  not  much,  in  cooling,  f  But  this  change 
in  volume  would  cause  strains,  and  the  new-formed  crust  would  be 
rent  and  shattered.  As  it  would  be  heavier  than  the  fluid  on  which 
it  had  formed,  these  fragments  might  be  engulfed,  and  perhaps 
again  melted  down  ;  but  as  the  fluid  would  be  already  in  a  viscous 
condition,  and  the  difference  in  specific  gravity  would  not  be  great, 
the  fragments  very  probably  would  continue  to  float,  and  after  a 
time  would  again  "  freeze  "  together.  The  description  given  by  Pro- 
fessor Dana  of  one  of  the  lakes  of  lava  in  the  crater  of  Kilauea 


*  A  stratified  arrangement,  according  to  Mr.  Lockyer,  is  exhibited  by  the  sun.  The 
planets  exterior  to  the  orbit  of  the  earth  are  composed  of  materials  lighter  than  it  ;  the  two 
nearer  to  the  sun  are  rather  heavier  in  proportion.  Even  in  the  earth  itself  the  atmo- 
sphAe,  the  water,  and  the  inner  mass  come  in  like  order. 

f  It  is  not  every  substance  (as  is  well  known)  that  contracts  in  cooling,  and  the  amount 
of  contraction  even  of  such  familiar  materials  as  basalt  or  trachyte  is  not  very  accurately 
determined,  but,  as  a  general  rule,  it  may  be  assumed  that  the  igneous  rocks  occupy  less 
space  in  a  solid  than  in  a  liquid  form. 


METEORS  AND    THE  EARTH'S  BEGINNING.  307 

may  serve  to  represent,  on  a  small  scale,  a  process  which  at  first 
would  be  very  general  over  large  areas  of  the  earth's  surface  :  * 

"  Although  mostly  crusted  over  [the  lake]  showed  the  red  fires 
in  a  few  long  crossing  lines  (fissures),  and  in  three  to  five  open 
places,  halfway  under  the  overhanging  rock  of  the  margin,  where 
the  lavas  were  dashing  up  in  spray,  and  splashing  noisily  with  seem- 
ingly the  liquidity  of  water.  Now  and  then  the  fireplaces  widened 
out  toward  the  interior  of  the  lake,  breaking  up  the  crust,  and  con- 
suming it  by  fusion.  .  .  Although  relatively  so  quiet,  the  mobil- 
ity of  the  brilliant  splashing  lavas  made  it  an  intensely  interesting 
sight.  Occasionally  the  red  fissures  widened  by  a  fusing  of  the  sides 
as  the  crust  near  by  heaved  and  the  lavas  flowed  over  the  surface. 
It  was  evident  from  the  cooled  streams  outside  that  now  and  then 
more  forcible  movements  take  place,  followed  by  outflows  over  the 
margin,  when  the  whole  lake  is  in  action." 

But  at  first  the  strains  of  the  shrinking  mass  and  the  pressure  of 
the  imprisoned  vapors  would  not  be  the  only  disturbers  of  the 
equilibrium  of  the  crust.  The  part  immediately  below  it,  whatever 
might  be  the  state  of  the  central  portion  of  the  globe,  would  be 
fluid — an  incandescent  ocean  many  miles,  at  least,  in  depth,  just 
frozen  over  at  the  surface.  This  liquid  mass  would  be  affected  by 
the  attraction  of  the  moon  (if  it  were  already  detached)  and  of  the 
sun,  which  at  that  time,  possibly,  might  be  augmented  in  bulk  by 
the  matter  which  is  now  condensed  into  Mercury  (supposing  Venus 
to  have  begun  an  independent  journey).  Round  and  round  the 
earth  a  great  tidal  wave  would  travel  in  this  molten  sea,  and  the 
crust  would  be  thrown  again  and  again  into  a  state  of  strain,  by 
which  it  might  be  repeatedly  ruptured  until  it  had  become  suffi- 
ciently thick  to  offer  an  adequate  resistance  to  these  recurrent 
disturbances. 

The  temperature  at  which  the  crust  would  begin  to  form  would 
probably  be  something  like  2000°  F.  This,  as  was  stated  in  a 
former  chapter,  f  is  a  rough  inference  from  observations  made  on 
lava  streams  as  they  are  cooling,  and  on  certain  rocks  as  they  are 
melted  artificially.  But  since  water,  under  ordinary  conditions, 
boils  at  212°  F.,  its  vapor  could  not  condense  and  remain  upon  the 
crust  until  the  latter  had  cooled  down  to  very  much  below  even 
a  dull  red  heat.  At  that  time  the  atmosphere  would  be  greatly 
heated ;  neither  ocean  nor  lake  nor  river  could  exist.  The  crust 

*  "  Characteristics  of  Volcanoes,"  p.  113.  f  P.  243. 


308  THE   STORY  OF  OUR  PLANET. 

must  have  long  ceased  to  glow ;  it  must  have  solidified  to  a 
moderate  depth  at  least  (though,  no  doubt,  substances  like  lava 
are  bad  conductors)  before  the  watery  envelope  could  begin  to 
form.  If  so,  the  crust  itself  must  have  solidified  under  conditions 
materially  different  from  those  of  a.  lava  stream  at  the  present  day ; 
for  not  only  is  crystallization  affected  by  pressure,  but  also  radiation 
would  be  then  comparatively  slow,  because  the  atmosphere  would 
differ  much  less  in  temperature  from  the  solidifying  rock  than  the 
air  now  does  from  the  surface  of  the  lava  stream.  The  crust  would 
probably  be  formed  in  all  cases  at  a  temperature  above  that  of 
"  white  heat,"  and  it  would  change  slowly  down  through  the 
various  grades  of  color  till  the  natural  tint  of  the"  constituent 
rock  was  assumed.  Yet,  even  then,  water  at  first  would  not  be  able 
to  rest  upon  it,  but  if  by  some  chance  the  vapor  in  the  atmosphere 
were  locally  condensed,  the  drops  of  boiling  rain  would  be  rejected 
hissing  from  the  uncongenial  surface.  But  what  would  this  mean  ? 
If  the  present  ocean  were  converted  into  vapor,  the  weight  of  the 
atmosphere  would  be  augmented  by  that  of  a  shell  of  water  of  the 
area  of  the  globe  and  two  miles  in  thickness  ;  or,  in  other  words, 
the  atmospheric  pressure  would  be  then  about  350  times  its  present 
amount.*  If  so,  even  a  lava  flow  would  consolidate  under  a  pres- 
sure equivalent  to  that  of  some  4000  feet  of  average  rock  ;  f  it 
would  be  in  a  condition  more  like  that  of  an  intrusive  "sill"  nearly 
three-quarters  of  a  mile  below  the  surface,  but  with  this  difference, 
that  the  process  of  cooling  would  be  slower,  because  the  tem- 
perature of  the  atmosphere  would  be  far  higher  than  that  of  the 
earth  is  now,  and  for  long  has  been,  at  this  depth.  Whether  any 
relics  of  this  primeval  crust  can  still  be  recognized  is  a  matter  on 
which  very  different  opinions  are  entertained  by  geologists ;  the 
majority,  probably,  would  answer  in  the  negative.  But  this  subject 
can  be  more  appropriately  noticed  in  a  future  chapter.  For  the 
present  it  may  suffice  to  indicate  the  general  character  of  the 
process  of  consolidation,  and  to  emphasize  the  fact  that  it  occurred 
under  circumstances  materially  different  from  those  which  can  have 
existed  in  the  immense  period  during  which  any  form  of  life  has 
been  present  on  the  earth.  No  doubt  a  universal  negative  is  a 
dangerous  thing  ;  and  a  man  has  endured  for  a  time  the  environ- 

*  The  increased  atmospheric  pressure  would  obviously  raise  the  boiling  point  of  water 
above  212°  F.,  and  so  allow  it  to  condense  at  a  higher  temperature  than  it  now  can  do, 
but  this  would  not  affect  the  general  argument  used  above. 

f  See  the  author's  "  Rede  Lecture"  for  1892,  printed  in  Nature,  vol.  xlvi.  p.  180. 


METEORS  AND    THE  EARTH'S  BEGINNING.  309 

merit  of  an  oven  hot  enough  to  cook  a  beefsteak  •  still,  it  may  be 
affirmed  that  the  earth  remained  void  of  life  so  long  as  the  tem- 
perature of  its  crust  exceeded  that  at  which  water  now  boils  at  the 
sea  level. 

Whatever  might  be  the  condition  of  the  great  interior  mass  of 
the  earth — whether  it  continued  liquid,  at  least  for  some  ages 
longer,  or  whether,  as  is  considered  more  probable  by  many  emi- 
nent physicists,  solidification  commenced  at  the  center,  in  conse- 
quence of  the  great  pressure  to  which  the  inmost  part  was  sub- 
jected, and  extended  outward  till  it  was  met,  so  to  say,  by  the 
thickening  skin — we  may  assume  an  original  liquidity  of  the  surface, 
and  pass  on  to  inquire  what  modification  this  would  undergo  in  the 
process  of  cooling.  So  many  matters  which  are  essential  factors  in 
the  investigation  are  so  little  known  at  present  that  all  inferences 
must  be  regarded  as  hardly  more  than  conjectures  and  provisional 
in  character ;  but  even  an  hypothesis  has  its  advantages  when  the 
data  are  insufficient  for  the  construction  of  a  theory,  since  it  serves 
to  direct  the  thoughts  and  suggest  the  lines  of  an  inquiry,  and 
brings  to  light  principles  of  which,  in  any  case,  some  account  must 
be  taken.  The  spots  which  occasionally  darken  the  sun's  face 
indicate  that  perfect  uniformity  does  not  prevail  even  under  condi- 
tions which  must  have  long  ceased  on  our  globe  at  the  epoch  now 
under  consideration,  and  that  not  inconsiderable  areas  of  the  solar 
envelope  are  in  a  state  different  from  that  of  the  rest.  So,  in  the 
case  of  the  earth,  when  it  first  solidified,  there  is  no  evidence  that 
every  part  of  its  vaporous  envelope  was  in  a  perfectly  uniform  con- 
dition, or  the  surface  beneath  it  completely  homogeneous  in  com- 
position and  in  state.  Some  parts  of  the  exterior,  owing  to 
unknown  reasons,  may  have  begun  to  solidify  slightly  in  advance 
of  others ;  and  even  after  a  crust  had  formed  over  the  whole,  this 
may  not  have  been  in  every  part  equally  strong  or  equally  thick. 
When  the  atmosphere  had  reached  its  present  condition,  if  not 
before,  the  heat  emitted  by  the  sun  must  have  had  more  effect  in 
equatorial  than  in  polar  regions,  so  that  the  crust  would  stiffen  and 
thicken  rather  more  rapidly  near  to  the  latter  than  near  to  the 
former.  Professor  Daubree  has  shown  by  some  interesting  experi- 
ments that  if,  when  a  globular  body  contracts,  its  crust  be  less 
flexible  in  some  parts  than  in  others,  its  regular  spherical  form 
is  not  retained,  but  a  deformation  takes  place,  which  depends  on 
the  difference  in  rigidity  of  the  material.  He  employed  in  his 
experiments  a  common  material  and  a  familiar  apparatus.  Every- 


3 1°  THE   STORY  OF  OUR  PLANET. 

one  knows  those  colored  balls  of  India  rubber  which  are  distended 
with  air  or  with  gas,  and  are  of  various  sizes,  from  about  five  to  ten 
inches  or  more  in  diameter.  The  child's  toy  was  pressed  into  the 
service  of  science.  Professor  Daubree  took  some  balls  of  the  larger 
size,  such  as  are  commonly  sold  in  Paris,  and  placed  on  their  ex- 
terior a  partial  coat  of  paint,  which  had  been  carefully  prepared  so 
as  to  adhere  perfectly  during  any  change  of  volume  of  the  ball. 
This  paint  was  applied,  not  irregularly,  but  in  definite  patterns,  to 
several  balls.  On  one  it  formed  a  broad  strip — a  kind  of  girdle — 
about  the  equator ;  on  another  it  was  arranged  in  zones  extending 
from  pole  to  pole,  corresponding  in  shape  with  the  spaces  between 
circles  of  longitude,  and  about  45°  in  width  ;  on  a  third  no  paint 
was  placed.  Some  of  the  air  was  then  allowed  to  escape.  The 
india  rubber  of  course  contracted.  In  the  last  .case  this  produced 
a  wrinkling  of  the  .surface  without  any  approach  to  regularity,  but 
obviously  influenced  by  accidental  results  of  the  processes  adopted 
-in  making  the  ball,  such  as  the  deposit  of  a  little  more  sulphur  in 
one  part  than  in  another.  But  in  the  other  two  cases — not  to  men- 
tion instances  where  the  paint  was  disposed  in  less  simple  patterns — 
the  effects  were  very  remarkable.  The  uncovered  portion  of  the 
india  rubber  contracted  more  than  that  which  had  been  stiffened  by 
paint.  The  latter  accordingly  bulged  up,  so  as  to  form  a  low 
mound,  in  section  like  a  very  flattened  arch,  and  across  this,  per- 
pendicular to  its  sides,  ran  a  series  of  many  small,  similarly  shaped 
undulations.  In  every  instance  the  part  covered  by  paint  rose  like 
a  low  island  above  the  level  of  the  rest,  and  was  always  traversed  by 
wrinkles,  which  ran  at  right  angles  to  its  external  boundary. 

These  experiments  indicate  that  if,  at  any  early  period  of  the 
earth's  history,  while  the  crust  was  still  comparatively  thin  and 
flexible,  and  the  loss  of  heat  and  consequent  contraction  were  corre- 
spondingly rapid,  certain  parts  had  become  distinctly  more  indurated 
than  others — it  matters  not  from  what  cause — this  fact  would  bring 
about  a  marked  deformation  of  the  surface  which  bore  a  direct  rela- 
tion to  the  disposition  of  the  harder  and  the  more  flexible  parts. 
The  one  would  be  upheaved  as  continental  masses,  the  other  would 
become  receptacles  for  the  ocean.  In  these  land  masses  the  rocks 
at  first  would  not  be  sharply  folded  or  violently  displaced,  but  rather 
would  be  bent  into  gently  undulating  curves.  It  is  a  fact,  which 
seems  to  be  not  without  significance,  that  this  structure  is  very 
characteristic  of  certain  rocks  which,  with  good  reason,  may  be  con- 
sidered to  be  some  of  the  oldest  known.  To  this  point,  however, 


METEORS  AND    THE  EARTH'S  BEGINNING.  311 

we  must  again  recur;  for  the  present  it  suffices  to  bear  in  mind  that 
any  irregularity  in  the  first  formed  crust  not  only  must  produce  an 
immediate  effect,  but  also  must  influence  the  result  of  all  further 
contraction.  Moreover,  when  once  the  sea  had  covered  portions  of 
the  crust,  these  would  radiate  heat  less  rapidly  than  the  parts  in 
direct  contact  with  the  atmosphere.  Under  the  former  the  crust 
would  increase  more  slowly  in  thickness,  and  thus  continue  to  be 
more  flexible  than  under  the  latter  or  land  parts.  Strain  in  the  one 
case  might  result  in  gradual  and  continuous  flexure,  tending  to 
augment  and  deepen  the  depression  already  formed  ;  in  the  other  it 
might  be  resisted  for  a  time,  with  the  ultimate  consequence  of  a 
more  sudden  yielding,  accompanied  by  crushing,  faulting,  and  all 
the  more  conspicuous  signs  of  disturbance.  But  we  must  abstain 
from  following  any  further  this  line  of  speculation  ;  for  the  processes 
of  Nature  already  described — the  results  of  denudation  and  deposi- 
tion— also  cannot  fail  to  produce  important  modifications  in  the 
strength  and  structure  of  the  crust,  and  the  subject  speedily  becomes 
so  complicated  that,  with  our  present  knowledge,  we  must  rest  con- 
tent with  calling  attention  to  causes  which  cannot  fail  to  have  pro- 
duced effects,  and  with  keeping  careful  watch  for  any  hints  which 
may  be  furnished  by  the  special  study  of  particular  districts. 

But,  it  may  be  asked,  is  there  any  proof  beyond  the  analogy  of 
other  celestial  bodies  that  this  earth  was  ever  so  intensely  heated 
that  its  whole  surface  may  have  resembled  an  ocean  of  lava? 
Does  the  globe  itself  testify  in  any  way  to  its  former  condition  ? 
Passing  by  these  analogies,  and  the  fact  that  the  spheroidal  shape 
of  our  planet  suggests  an  original  flexibility,  which  is  more  naturally 
ascribed  to  heat  than  to  any  other  cause,  we  may  seek  an  answer  to 
the  question  from  the  earth  itself.  If  it  has  cooled  down  to  its 
present  condition  from  incandescence,  the  interior  should  be  still 
very  hot.  Direct  experiment  will  not,  of  course,  take  us  very  far, 
but  if  all  the  evidence  which  can  be  obtained  points  in  one  direction, 
and  if  the  conclusion  which  it  suggests  can  be  supported  by  indirect 
reasoning,  a  well-grounded  confidence  may  be  felt  in  the  accuracy 
of  our  induction. 

Let  us  briefly  review  this  evidence.  In  the  first  place  the  temper- 
ature of  water  from  deep-seated  springs  or  wells  is  barely  or  not  at  all 
affected  by  the  diurnal  or  annual  variation  of  temperature.  In  the 
well  of  Crenelle  the  water,  which  rises  from  a  depth  of  more  than 
1300  feet  below  the  surface,  is  at  the  same  temperature  in  January  as 
in  July,  and  at  any  place  the  water  from  a  deep  well  is  warmer  than 


312  THE   STORY  OF  OUR  PLANET. 

that  from  a  shallow  one.  Borings  have  been  made  and  shafts  have 
been  sunk  into  the  earth's  crust  to  a  depth  frequently  of  more  than 
a  thousand  feet,  occasionally  of  more  than  two  thousand,  and  in  one 
or  two  cases  exceeding  three  thousand.  The  Mont  Cenis  tunnel,  at 
its  greatest  distance  from  the  surface  of  the  ground,  is  5280  feet 
below  the  crest  of  the  Alps,  and  the  St.  Gothard  tunnel  in  like  man- 
ner reaches  a  distance  of  5578  feet;  that  is  to  say,  opportunities 
have  been  afforded  of  ascertaining  experimentally  the  temperature  of 
the  crust  of  the  earth  down  to  a  depth  of  about  a  mile.  In  all  these 
cases  the  result  is  the  same,  that  after  reaching  a  distance  from  the 
surface,*  at  which  the  fluctuations  in  temperature — whether  diurnal 
or  annual — due  to  the  increase  or  decrease  of  the  heat  received  from 
the  sun,  are  no  longer  perceptible  (generally  about  sixty  feet  beneath 
the  surface),  the  temperature  invariably  increases  with  the  depth. 
The  rate  of  increase  is  subject  to  considerable  variation ;  it  is 
affected,  as  might  be  expected,  by  the  conductivity  of  the  rocks,  by 
their  mineral  composition  and  arrangement,  and  by  local  circum- 
stances not  always  easy  to  determine.  For  instance,  it-  may  be  as 
low  as  i°  F.  for  every  82  feet  of  descent,  on  the  average,f  or  as 
rapid  as  i°  F.  for  34  feet;:}:  but  the  great  majority  of  the  observa- 
tions give  averages  not  far  away  from  i°  F.  to  60  feet.  The  Com- 
mittee of  the  British  Association  after  discussing  a  large  number  of 
observations  came  to  the  conclusion  that  i°  F.  in  64  feet  was  a  fairly 
safe  average.§  So  for  a  certain,  though  a  limited,  distance  the  crust 
of  the  earth -evidently  becomes  hotter  as  the  depth  from  the  surface 
increases,  and  the  rise  is  such  as  might  be  expected  if  the  inner  mass 
were  at  a  high  temperature  and  losing  heat  by  radiation. 

Another  consideration  of  a  more  general  character  points  to  the 
same  conclusion.  If  the  earth  be  regarded  as  consisting  of  a  series 
of  concentric  shells,  each  of  these  has  to  support  the  weight  of  all 
those  above  it.  Pressure  accordingly  increases  in  proportion  with 
the  distance  from  the  surface.  Every  deep  coal  mine  affords  proof 
of  the  truth  of  this  statement,  for  when  some  part  of  a  seam  has  been 


*The  depth  of  the  Sperenberg  boring,  chiefly  in  rock  salt,  at  which  observations  were 
made  was  3492  feet ;  that  of  a  coal  pit  at  St.  Andre  du  Poirier  is  3084  feet. 

f  This  is  in  the  St.  Gothard  tunnel,  and  the  increase  in  the  Cenis  tunnel  is  only  i°  F.  in 
79  feet.  In  a  pit  at  Dukinfield  (2700  feet)  it  is  i°  F.  in  72  feet  ;  in  another  at  Wigan 
(2424  feet)  it  is  1°  F.  in  79  feet ;  but  in  one  of  the  pits  at  St.  Andre  du  Poirier  (2952  feet) 
it  does  not  exceed  1°  F.  in  116  feet — a  most  exceptional  slowness. 

\  A  mine  at  Weardale,  in  Northumberland. 

§  See  "  British  Association  Report,"  1881,  p.  88. 


METEORS  AND    THE  EARTH'S  BEGINNING.  313 

worked  away,  the  floor  of  the  excavation  bulges  up,  the  roof  "  sags  " 
down,  and  the  walls  begin  to  be  crushed  by  the  tremendous  pres- 
sure of  the  overlying  strata.  If  this  is  so  great  that  in  a  mine  at 
Dukinfield,  2500  feet  below  the  surface,  a  brick  arch,  four  feet  in 
thickness  and  of  no  great  span,  has  been  actually  crushed  in,  what 
must  it  become  at  a  distance  of  several  miles?  Estimates  have  been 
made*  of  the  effects  of  compression  on  the  assumption  that  the 
inner  parts  of  the  earth  are  composed  of  materials  similar  to  those 
of  its  crust,  and  it  has  been  ascertained  that  its  density  would  grad- 
ually increase,  until  at  a  depth  of  2000  miles  (about  halfway  down) 
it  would  be  thrice  that  of  the  surface — in  other  words,  clay  would 
be  compressed  till  it  was  as  heavy  as  iron,  while  at  the  center  it 
would  be  almost  four  times  its  original  weight.  On  the  supposition 
that  the  law  of  density,  on  which  these  statements  are  founded, 
holds  good,  the  weight  of  the  earth  can  be  calculated,  and  the  result 
obtained  is  considerably  in  excess  of  the  actual  weight.  Hence 
there  must  be  either  something  very  abnormal  in  the  composition 
of  the  interior,  or  some  force  in  operation  to  counteract  the  effects 
of  pressure,  and  this  would  be  done  very  effectually  by  heat.  It 
must  not,  however,  be  assumed  that  the  temperature  continues  to 
increase,  as  the  center  of  the  earth  is  approached,  at  anything  like 
the  rate  which  has  been  inferred  from  the  observations  already 
mentioned.  If  so,  the  heat  at  a  very  few  hundred  miles  from  the 
surface  would  be  almost  inconceivably  great,  enough  to  fuse  the 
most  refractory  substances  known  in  our  laboratories,  and  further 
down  might  even  rival  that  of  the  sun.  Lord  Kelvin  has  investi- 
gated the  question  on  the  assumption  that  the  globe  is  a  cooling 
mass,  and  has  found  that  after  a  depth  of  a  few  miles  the  increase  of 
the  earth's  temperature  becomes  less  and  less  rapid.  If,  near  the 
surface,  it  be  i°  F.  for  every  51  feet  of  descent  (probably  rather  too 
liberal  an  estimate),f  this  would  hold  good,  roughly,  down  to  about 
20  miles ;  but  at  a  depth  of  about  80  miles  the  increase  would  be 
reduced  to  i°  F.  in  141  feet,  and  at  about  double  that  distance  from 
the  surface  it  would  not  be  more  than  i°  F.  in  2250  feet,  after  which 
it  would  go  on  in  a  rapidly  diminishing  ratio.  Still,  in  any  case,  at 
a  comparatively  moderate  depth — for  instance,  from  about  25  to  30 

*  By  the  eminent  mathematician  Laplace,  author  of  the  "  Traite  de  Me'canique  Celeste," 
who  died  in  1827. 

f  This  was  in  accordance  with  the  older  observations,  in  which  certain  precautions  were 
not  observed.  The  more  accurate  methods  adopted  of  late  years  have  tended  to  reduce 
the  rate  to  that  stated  above. 


314  THE   STORY  OF  OUR  PLANET. 

miles — a  temperature  would  exist  which  would  suffice  at  the  surface 
to  fuse  most  rock,  for  at  the  latter  depth  the  calculated  result  would 
be  3147°  F.  Of  course  there  would  be  a  considerably  increased 
pressure,  which  would  raise  the  fusing  point  of  the  rock,  but  the 
density  would  not  be  so  greatly  altered  as  to  produce  a  very  marked 
difference;  for  even  at  250  miles  it  has  only  risen  to  3.1  if  the 
average  on  the  surface  be  taken  at  2.5.  It  is  therefore  possible 
that  the  material  of  the  earth  may  not  remain  solid  for  more  than  a 
very  moderate  distance  from  the  surface.  Pressure  and  tempera- 
ture are  acting  in  antagonism,  and  the  latter  may  prevail  over  the 
former.  This  suggests-  the  inquiry,  What  is  the  condition  of  the 
earth's  interior — is  it  liquid,  or  does  it,  after  a  zone  which  is  melted 
by  the  increasing  temperature,  again  become  solid  through  pressure, 
or  is  it  solid  throughout? 

This  fascinating,  but  extremely  difficult,  problem  belongs  to  the 
province  of  mathematical  physics,  and  so  lies  outside  that  of  the 
geologist,  though  his  special  researches  may  enable  him  to  contribute 
toward  its  solution  certain  facts  which  cannot  be  left  out  of  con- 
sideration. It  has,  however,  engaged  the  attention  of  several 
eminent  men  of  science,  and  they  are  by  no  means  in  accord  in 
their  conclusions ;  for  though  the  method  adopted  may  be  unim- 
peachable, sundry  data  are  necessary  in  the  investigation  which  are 
at  present  by  no  means  determined  with  certainty.  As  Professor 
Huxley  once  remarked,  in  so  many  words,*  the  value  of  the  grist 
from  the  mathematical  mill  depends  upon  the  quality  of  the  corn 
which  is  put  into  the  hopper ;  hence  while  some,  like  Lord  Kelvin, 
have  come  to  the  conclusion  that  the  earth  is  solid  throughout, 
others,  like  Hennessy,  have  maintained  that  the  crust  may  not  be 
more  than  some  twenty  miles  thick,  and  that  all  within  it  is  fluid ; 
others  adopt  a  tertium  quid,  and  are  of  opinion  that,  after  an  interval 
of  fluidity,  the  mass  again  passes  back  into  a  solid  condition. 

Though  mathematicians  are  not  unanimous,  the  majority  seem 
inclined  to  regard  the  earth  as  practically  solid,  while  the  idea  of  a 
rather  thin  crust  finds,  perhaps,  more  favor  among  geologists. 
With  the  former  two  arguments  for  a  long  time  evidently  carried 
great  weight.  The  one  is  founded  on  the  so-called  precessional 
movement  of  the  earth's  axis,  which  does  not  remain  parallel  to 
itself  at  every  point  of  the  orbit.  What  happens  may  be  most 
readily  understood  from  a  model  of  a  solar  system,  such  as  one  of 

*  Presidential  Address  to  the  Geological  Society,  vol.  xxv.  1869,  p.  i. 


METEORS  AND    THE  EARTH'S  BEGINNING.  315 

the  old-fashioned  orrerys.  Suppose  the  axis  about  which  the  earth 
turns  to  be  represented  by  a  straight  wire,  like  a  knitting  needle, 
thrust  through  the  model  globe,  and  that  another  wire,  at  any  mo- 
ment, is  run  parallel  to  it  through  the  sun.  If  the  two  are  con- 
strained to  keep  always  parallel,  one  to  another,  the  latter,  by  its 
movement,  will  conveniently  indicate  the  changes  of  position  in 
the  former.  If  the  earth's  axis  remained  parallel  to  itself  in  every 
part  of  its  orbit,  this  line  would  be  unmoved.  But,  on  the  contrary, 
it  moves  slowly  onward :  it  sweeps  out  in  space  a  conical  surface, 
and  completes  an  entire  revolution  once  in  25,898  years.  The  pre- 
cessional  movement  thus  represented  is  produced  by  the  attraction 
of  the  sun  and  moon  on  the  protuberant  matter  in  the  equatorial 
region  of  the  earth.  If  this  latter  were  a  true  sphere,  no  such 
movement  would  exist ;  sun  and  moon,  as  it  were,  pluck  at  the 
earth's  girdle  while  it  goes  spinning  round,  and  the  "jerk  "  makes  it 
stagger.  When  a  top  is  "  asleep  "  a  similar  movement  can  be  pro- 
duced by  tapping  it  gently  with  a  knitting  needle.  The  amount  of 
precession  can  be  calculated  theoretically  ;  it  depends  upon  the 
mass  of  the  inner  sphere,  which  the  outer  girdle  must,  so  to  say, 
carry  along  with  itself.  If  the  earth  consisted  of  a  fluid  incased 
in  a  solid  shell,  and  the  latter  could  turn  upon  the  former  with  little 
or  no  friction,  then  the  precession  would  be  much  greater  than  it  is 
at  present,  because  the  inner  mass  would  be  comparatively  inef- 
fective as  a  "  drag "  against  the  disturbing  influence  of  the  outer 
ring.  It  was  maintained  by  the  late  Mr.  Hopkins  that  the  observed 
amount  of  precession  indicated  that  the  earth's  crust  must  be  at 
least  from  800  to  1000  miles  thick,  and  the  globe,  as  a  whole,  not 
less  rigid  than  glass,  and  this  view  was  supported  by  Lord  Kelvin  ; 
but  recent  investigations  have  tended  to  weaken  the  arguments  in 
favor  of  the  earth's  solidity,  so  far  as  they  rest  on  precession,  for 
Professor  G.  Darwin  has  shown  that,  in  certain  cases,  the  preces- 
sional  movement  in  a  fluid  spheroid  is  the  same  as  that  in  a 
rigid  one. 

The  other  argument  is  founded  on  the  tides.  The  combined 
attraction  of  the  sun  and  moon,  as  already  described,  produces  a 
wave  which  travels  round  the  globe.  The  water,  so  to  say,  is  lifted 
up  from  the  crust  into  a  heap,  and  thus  rises  and  falls  against  the 
land,  which  is  fixed  in  position.  But  if  the  crust  were  flexible,  it 
would  yield  to  the  attraction  like  the  water;  it  too  would  have 
its  own  tidal  wave,  and  that  in  the  ocean  would  be  no  longer 
perceptible,  since  the  land  would  rise  and  fall  with  the  water. 


316  THE   STORY  OF  OUR  PLACET. 

In  order  that  tides  should  be  as  they  are  at  present,  the  globe 
must  be  not  less  rigid  than  steel  ;  so  that,  if  not  wholly  solid, 
it  must  at  least  have  a  crust  more  than  a  thousand  miles  in 
thickness. 

The  arguments — if  the  question  be  regarded  from  the  geologist's 
point  of  view — on  the  whole,  seem  favorable  to  the  existence,  at 
any  rate,  of  a  fluid  zone  at  no  very  great  depth.  It  is  admitted 
that,  at  a  distance  of  from  twenty-five  to  thirty  miles  a  tempera- 
ture should  be  reached  which  probably  would  be  sufficient  to  fuse 
most,  if  not  all,  rocks  and  very  many  metals,  even  under  the  in- 
creased pressure.  He  observes  in  mountain  chains  the  evidence 
of  intense  lateral  thrusting,  which  seems  most  naturally  and  simply 
explained  by  contraction  of  the  crust.  The  amount,  however,  of 
this  is  considerable  ;  the  formation  of  an  important  chain  frequently 
implies  the  diminution  of  the  earth's  surface  by  an  area  at  least  three 
or  four  hundred  miles  in  length,  and  from  sixty  to  a  hundred  in 
width.  When  it  is  remembered  that  mountain  chains  have  been 
developed,  probably  from  the  most  remote  period,  at  various  times 
in  the  earth's  history,  doubts  arise  whether  these  do  not  indicate  a 
reduction  in  volume  more  than  can  be  explained  on  the  hypothesis 
that  the  earth  both  is  and  has  been  a  solid  body  losing  heat  by 
radiation.  This  certainly  is  a  difficulty,  but  it  may  not  be  insuper- 
able. A  very  small  diminution  in  the  earth's  radius,  supposing  the 
effect  to  be  concentrated  on  a  single  zone  of  its  crust,  would  give 
birth  to  a  considerable  mountain  chain.  As  against  this  it  may  be 
fairly  urged  that  we  have  no  right  to  assume  that  the  effect  of  a 
general  contraction  will  be  concentrated  on  a  single  locality,  and 
that  even  on  this  hypothesis  the  amount  required  would  be  too 
large. 

A  few  years  since  Mr.  C.  Davison  called  attention  to  the  distribu- 
tion of  strain  in  the  outer  part  of  a  solid  globe  which  was  losing 
heat  by  radiation.*  He  showed  that  the  exterior  portion  of  the 
crust  would  be  in  a  state  of  compression,  but  that  this  would  gradu- 
ally diminish  in  amount,  until,  at  a  very  moderate  depth,  it  vanished. 
Below  this  level  the  direction  of  the  force  would  be  reversed,  and 
the  rocks  be  in  a  condition  of  extension.  On  the  assumption  that 
the  globe  was  cooling  under  conditions  perfectly  uniform,  this  "  zone 
of  zero  strain,"  as  it  is  termed  by  Mr.  Davison,  would  lie  at  a  depth 
of  only  about  five  or  six  miles.  If  this  be  so,  then  the  process  of 

*  Gt-ol.  Magazine,   1889,  p.   220. 


METEORS  AND    THE  EARTITS  BEGINNING.  317 

mountain  making  must  be  concentrated  into  a  very  limited  thickness 
of  the  crust,  and  be  very  superficial  in  character  as  compared  with 
the  globe  as  a  whole.  That,  at  any  rate,  even  the  mightiest  moun- 
tain chain  is  but  a  trifling  rugosity  compared  with  the  vast  mass  of 
the  earth  has  been  already  indicated  in  a  former  chapter.* 

So  we  must  confess  that,  when  we  review  the  whole  question  of 
the  condition  of  the  earth's  interior,  it  seems  impossible,  at  present, 
to  come  to  any  definite  conclusion.  Many  geological  phenomena, 
as  Mr.  O.  Fisher  has  maintained,  f  would  be  more  easily  explained 
on  the  hypothesis  that  a  fluid  interior  underlies  a  comparatively  thin 
crust ;  but  the  conclusions  of  mathematicians,  though  they  rest,  it 
must  be  admitted,  on  data  which  are  not  beyond  question,  are 
generally  favorable  to  the  solidity  of  the  globe  as  a  whole.  This, 
however,  seems  to  be  certain,  that  at  a  moderate  depth  beneath  the 
surface — thirty  miles  at  most,  and  perhaps  less — a  zone  must  exist 
at  which  the  rocks,  if  not  actually  melted,  must  be  very  nearly  at 
their  melting  point,  so  that  they  might  pass,  in  consequence  of  a 
very  slight  change  in  their  condition,  from  solid  to  liquid,  or  the 
reverse.  It  must  be  also  remembered  that  the  melting  point  of  a 
rock  is  very  sensibly  affected  by  the  presence  of  water.  The 
investigations  df  Guthrie,  Lagorio,  and  others:}:  prove  that  water,  in 
many  cases,  greatly  lowers  the  melting  point  of  both  minerals  and 
rocks.  Hence  its  access  may  cause  a  mass  of  rock,  which  is  already 
at  a  high  temperature,  to  change  from  a  solid  to  a  liquid  condition, 
and  by  the  escape  of  water  the  opposite  result  may  be  brought  about. 
By  capillary  attraction  water  may  pass  downward  to  considerable 
depths  in  the  direction  of  a  heated  mass,  even  where  access  cannot 
be  obtained  through  fissures  or  any  kind  of  divisional  planes ;  and 
besides  this,  there  is  no  reason  to  suppose  that  its  vapor,  or  at  any 
rate  its  constituent  gases,  oxygen  and  hydrogen,  were  restricted, 
when  the  mass  first  condensed,  to  its  outer  layers ;  they  may  have 
been  entangled  more  or  less  completely  in  the  inner  portions,  so 
that  they  may  be  still  diffused  in  the  materials  of  the  globe,  at  least 
to  a  very  considerable  depth. 

*  P.  12-15. 

f  In  a  volume  entitled  "  The  Physics  of  the  Earth's  Crust." 

\  Of  these  a  good  summary  is  given  in  Mr.  J.  J.  H.  Teall's  British  "  Petography," 
ch.  xiii. 


CHAPTER    II. 

THE  ERAS  AND    SUBDIVISIONS    IN  GEOLOGICAL   HISTORY. 

WHEN  an  attempt  was  first  made  to  apply  scientific  principles  to 
the  elucidation  of  the  earth's  history,  the  task  of  the  geologist 
closely  resembled  that  of  the  archaeologist  as  he  disinters  the  site 
of  a  city  in  the  land  of  an  almost  unknown  people.  Before  the 
ground  is  broken  he  sees  nothing  more  than  some  shapeless  mounds 
or  confused  piles  of  ruins ;  where  once  a  stately  palace  may  have 
risen,  grass  now  grows  green  ;  where  once  the  altar  smoked  with 
sacrifices,  the  bird  has  made  its  nest  and  rears  its  young ;  where  the 
streets  once  resounded  with  the  steps  of  a  thronging  multitude,  only 
the  jackal's  howl  wakes  the  silent  echoes.  But  as  the  work  of  the 
spade  proceeds,  as  the  trenches  are  lengthened  and  deepened,  coins, 
ornaments,  weapons,  inscriptions,  and  sculptures  are  unearthed  ;  the 
remnants  of  walls  and  the  ground  plans  of  buildings  are  laid  bare. 
Beneath  the  floor  of  one  structure  the  foundations  of  another  may 
be  discovered.  Beneath  a  layer  characterized  by  one  group  of 
articles  another  may  be  disclosed  containing  objects  of  a  different 
type.  That  the  relics  which  are  discovered  near  to  the  surface  are 
newer  than  those  found  only  at  a  considerable  depth  is  an  obvious 
inference  ;  it  is  certain  that  fragments  of  carved  work  built  into  the 
walls  of  one  building  must  have  been  appropriated  from  another  of 
earlier  date.  From  such  investigations  the  groundwork  of  a  chrono- 
logical order  is  established  ;  by  a  study  of  the  inscriptions  on  coins 
and  of  the  works  of  art  in  general  some  progress  is  made  in  filling 
up  its  details.  But  to  render  the  history  anything  like  complete 
operations  of  a  similar  kind  must  be  undertaken  in  several  places. 
The  coins,  weapons,  ornaments,  and  utensils  of  whatever  material, 
the  graven  patterns,  the  sculpture  and  architectural  details,  must  be 
subjected  to  a  minute  and  comparative  study.  Then  the  wealth  of 
one  locality  supplements  the  poverty  of  another;  the  light  which 
shines  from  the  one  dispels  the  fog  which  hung  over  the  over.  The 
evidence  which  is  tendered  by  all  in  common,  like  a  "  bonding 
course  "  in  masonry,  strengthens  the  fabric  of  scientific  inference, 


THE  ERAS  IN  GEOLOGICAL   HISTORY.  319 

and  enables  the  archaeologist  and  historian,  as  the  area  of  observa- 
tion is  widened,  to  piece  together  in  an  orderly  succession  the 
information  which  once  appeared  so  fragmental  and  confused.  The 
tablets  graven  on  the  crags  which  overlook  the  sea  near  the  valley 
of  the  Nahr-el-Kelb  connect  the  histories  of  Egypt  and  Assyria  with 
that  of  Palestine,  while  the  study  of  monuments  and  cylinders, 
chiefly  during  the  last  half  century,  has  revealed  many  a  lost  chap- 
ter in  the  history  of  nations,  has  changed  the  "  children  of  Heth  " 
from  a  scattered  tribe  to  a  powerful  people,  and  not  only  has  revived 
the  forgotten  names  of  the  races  of  Shumir  and  Accad,  but  also  has 
brought  their  bodily  forms  to  light. 

On  lines  such  as  those  which  the  archaeologist  is  following  the 
geologist  has  worked.  In  each  district  a  chronological  succession 
is  inferred  from  the  order  in  which  the  strata  are  superimposed. 
Due  allowance  has  to  be  made  for  disturbances  such  as  are  produced 
by  the  intrusion  of  igneous  rocks,  by  faults,  and  the  like ;  localities 
suitable  for  study  have  to  be  selected,  regions  where  appearances 
may  be  deceptive  must  be  for  a  time  carefully  avoided,  until,  at 
each  place,  the  order  of  succession  in  the  various  strata  is  estab- 
lished, and  the  organic  remains  characteristic  of  each  are  determined. 
Then,  after  enlarging  the  area  of  study,  one  district  may  be  co-ordi- 
nated with  another,  and  the  history  by  this  means  both  extended 
in  scope  and  rendered  more  complete  in  detail.  It  is  here  as  in 
archaeology ;  at  this  or  that  place  gaps  may  exist  in  the  record  ; 
epochs  may  have  passed  of  which  no  memorial  has  been  preserved. 
Cities  for  a  time  may  have  been  desolate,  and  their  history  a  blank, 
as  was  that  of  Jerusalem  when  its  people  had  been  led  captive  to 
Babylon,  or  of  Aquas  Solis  while  Britain  was  becoming  England. 
At  one  site  the  story  may  be  cut  short  at  an  early  date,  as  it  is  at 
the  mounds  of  Hissarlik  or  of  Nineveh ;  at  another  it  may  be  con- 
tinuous, though  with  occasional  interruptions,  from  very  ancient 
times.  So  is  it  with  geology.  In  this  place  the  record  may  have 
been  speedily  closed  ;  in  that  it  may  have  begun  anew,  after  a  long 
interruption  ;  in  a  third  it  may  be  continuous.  But  in  the  first  and 
second  cases  the  gaps  which  exist  in  one  district  may  be  filled  up 
from  another  by  means  of  the  study  of  fossils,  and  the  history  of 
the  earth  as  a  whole  be  rendered  fairly  complete. 

Fossils,  then,  to  use  a  happy  phrase,  are  the  "medals  of  creation." 
They  are  to  the  stratigrapher  what  coins  and  inscriptions  are  to  the 
archaeologist  and  the  historian — the  means  of  restoring  order  to 
confusion  and  of  making  chronology  possible.  They  are,  however, 


320 


THE   STORY  OF  OUR  PLANET. 


more  than  this  ;  for  they  have  also  a  tale  to  tell  as  to  the  history  of 
life  and  its  development.  Strange  as  the  forms  may  be  which 
science  builds  up  when  it  bids  the  dry  bones  live,  almost  grotesque 
as  the  creatures  of  a  dream,  these  fall  into  their  place  in  that  great 


FIG.  120. — SOME  OF  THE  LATEST  FOSSILS.    (FROM  THE  SCOTTISH  GLACIAL  CLAYS.) 

i.  Saxicava  rugosa.  2.  Astarte  borealis  (a,  exterior  of  valve ;  b,  interior  of  valve).  3.  Pecte* 
islandicus.  4.  Leda  truncata  (a,  exterior  of  left  valve  ;  i,interior  of  left  valve).  5.  Tellina  calcarea, 
O,  exterior  of  left  valve  ;  £,  interior  of  left  valve).  6.  Led*  lanceolata.  ^.  Trophon  clathratum. 
8.  Natica  clausa. 

procession  which  unites  the  embryonic  forms  of  long  past  aeons 
with  the  perfected  types  of  the  present  age. 

But  it  may  be  asked,  What  is  a  fossil  ?  Though  the  term  is  in 
such  familiar  use,  it  is  not  a  very  easy  one  to  define  with  precision. 
It  means,  of  course,  something  dug  up,  with  the  limitation,  how- 
ever, that  this  must  have  been  once  alive,  or  a  part  of  a  living  thing. 
It  would  not  now  be  applied  to  a  crystal  or  a  concretion,  not  even 
to  one  of  those  very  ancient  tools  rudely  chipped  from  a  flint, 
though  this  might  be  called  a  relic  of  fossil  man.*  The  term  also 
implies  a  considerable  antiquity.  The  shell  of  an  oyster  dug  up 
from  the  refuse  heap  of  a  Roman  villa,  the  antler  of  a  stag  from  the 
site  of  a  pile  dwelling  on  a  Swiss  lake,  the  skeleton  of  a  man 
exhumed  from  a  tumulus  of  an  age  even  earlier  than  written  his- 
tory, would  not  be  called  a  fossil,  though  the  term  might  be  applied 
to  a  bone  of  one  of  his  more  savage  predecessors  who  hunted  the 

*  Marks  such  as  footprints,  worm  castings,  or  burrows,  and  the  like  are  often  preserved, 
and  are  commonly  reckoned  with  fossils. 


THE   ERAS  IN   GEOLOGICAL   HISTORY. 


321 


FIG.  121. — A  GROUP  OF 
CRYSTALS  (QUARTZ). 


mammoth  in  days  before  England  had  become  an  island.  The 
appearance  of  man  brings  us  very  near  the  time  limit  which  custom 
has  imposed  on  the  term. 

Fossils  are  preserved  in  more  than  one  way.  Sometimes,  as  in 
certain  gravels  and  clays,  they  differ  from  a  shell  or  bone  which 
quite  recently  has  formed  part  of  a  living  organism  only  in  having 
lost  more  or  less  animal  matter,  and  being 
thus  rendered  more  brittle  and  friable.  In 
certain  clays,  such  as  that  at  Bracklesham, 
mentioned  at  the  beginning  of  this  book, 
the  shells  often  are  so  "  rotten  "  that  they 
would  speedily  crumble  away  if  they  were 
not  hardened  by  being  first  thoroughly 
soaked  in  gum  or  in  a  preparation  of  isin- 
glass, and  then  allowed  to  dry.  Sometimes, 
as  in  the  case  of  peat  and  lignite,  certain 
further  chemical  changes  have  occurred, 
and  an  approach  is  made  to  the  second 
and  commoner  method  of  preservation, 
when  they  are  mineralized.  This  process 
may  be  effected  either  by  an  addition  of  that  chemical  constituent 
of  which  already  the  organism  chiefly  consists,  or  by  the  substitu- 
tion for  it  of  some  other  substance.  Thus  the  shell  of  a  mollusk 
from  the  Chalk  is  sometimes  so  completely  converted  into  carbonate 
of  lime  that  it  may  exhibit,  on  a  fractured  surface,  the  mineral 
cleavage  of  calcite,  yet  a  similar  shell  in  some  other  formation  may 
be  entirely  converted  into  phosphate  of  lime  or  chalcedony.*  In 
the  latter  case  the  original  constituents  of  the  shell  have  been  par- 
tially or  wholly  removed,  molecule  by  molecule,  and  replaced  by  a 
different  substance,  till  a  model  has  been  produced  which  sometimes 
is  so  exact  as  to  retain  even  the  most  delicate  structures.  Other 
minerals  besides  these  two  do  the  same  work,  such  as  marcasite, 
pyrite,  chalybite,  gypsum,  glauconite,  and  several  more,  which,  how- 
ever, are  even  less  frequent  than  the  two  last  named. f 

But  when  a  particular  stratum  or  group  of  strata  has  been  placed 
in  its  right  chronological  sequence,  and  can  be  identified  by  its 

*  Calcite  is  a  crystallized  form  of  carbonate  of  lime  ;  chalcedony  is  minutely  crystalline 
quartz. 

f  Marcasite  and  pyrite  are  forms  of  iron  sulphide  ;  chalybite  is  carbonate  of  iron  ;  gyp- 
sum is  hydrous  sulphate  of  lime  ;  glauconite  consists  of  silica,  alumina,  iron,  potash,  water, 
and  small  amounts  of  other  substances. 


322 


THE   STORY  OF  OUR  PLANET. 


characteristic  fossils,  when  it  can  be  recognized  by  this  means  in 
districts  far  apart,  which  perhaps  are  severed  by  physical  barriers, 
such  as  mountains  or  seas,  a  name  becomes  a  necessity,  if  only  for 
ready  designation.  Had  it  been  possible  at  the  outset  to  adopt 
some  principles  of  nomenclature  obvious  advantages  would  have 
followed,  because  names  would  have  been  excluded  which  were 


FIG.  122.— PALAEOLITHIC  FLINT  IMPLEMENTS,  FROM  ST.  ACHEUL,  NEAR  AMIENS. 

misleading,  barbarous,  or  absurd.  But  geology,  like  the  famous 
Topsy,  has  "  growed  " ;  it  has  been  always  the  least  orderly  and 
systematic  of  the  natural  sciences.  The  man  or  the  junta  has  not 
yet  arisen  sufficiently  powerful  to  sweep  away  the  relics  of  barbar- 
ism and  introduce  a  "  Code  Napoleon."  Thus  geological  nomen- 
clature follows  no  definite  principle,  and  in  it,  as  in  this  world,  good 
and  bad  are  mingled  together.  Sometimes  a  group  of  stratified 
rocks  is  named  from  some  lithological  peculiarity — as  the  Green- 
sand  or  the  Oolite,  the  Cretaceous  (chalky)  or  the  Carboniferous 
(coal-bearing)  system.  A  name  thus  selected  is  thoroughly  objec- 
tionable, because  it  is  only  locally  appropriate.  Chalk,  for  instance, 
is  only  found  in  certain  parts  of  Europe;  in  others  sandstones  or 
clays  were  being  simultaneously  formed.  This  is  occasionally  made 
even  worse  by  adopting  some  rustic  or  provincial  term  for  the  rock, 
such  as  Lias  or  Cornbrash,  Gault  or  Crag.  Some  names  indicate  a 
local  characteristic  in  a  broader  sense,  such  as  Dyas  or  Trias,  SQ 


324  THE   STORY  OF  OUR  PLANET. 

called  because  either  two  or  three  well-marked  divisions  can  be 
observed  in  the  one  connected  series.  Other  names  imply  a  chrono- 
logical position,  such  as  Eocene  or  Miocene;  but  this  method  is 
apt  to  lead  into  difficulties,  for  the  number  of  comparative  terms  is 
necessarily  limited.  A  name  founded  upon  that  of  some  district  or 
place  which  exhibits  a  very  fine  and  typical  section  of  the  particular 
set  of  strata  is  least  open  to  criticism — such  as  Cambrian  or  Silu- 
rian or  Jurassic  or  Portlandian  or  Kimeridgian — because  this  name 
merely  states  an  important  fact,  and  does  not  suggest  any  mislead- 
ing idea ;  and  it  can  be  dropped,  if  any  more  characteristic  locality 
be  found,  no  less  easily  than  another.  Doubtless  the  matter  is  not 
one  of  the  highest  moment.  Facts  are  more  important  than  words, 
and  a  "  rose  by  any  other  name  will  smell  as  sweet."  Still  an 
unsystematic  nomenclature  is  apt  to  give  rise  to  slovenly  thinking; 
and  geology,  as  experience  has  shown,  is  not  a  science  which  can 
afford  to  dispense  with  any  safeguard  favorable  to  precision  in 
reasoning. 

Whenever  a  bed  of  rock  is  sufficiently  characterized  by  its  fossils, 
or  in  the  absence  of  these  by  its  mineral  contents,  a  name  becomes 
desirable  for  purposes  of  reference,  as  a  counter  in  the  verbal  cur- 
rency expressive  of  a  group  of  ideas.  The  smallest  mass  which  can 
be  thus  conveniently  distinguished  from  others  becomes  the  geolog- 
ical unit.  For  such  a  one  the  name  of  a  Stage  has  been  proposed. 
A  number  of  these  masses  which  exhibit  many  common  character- 
istics, but  are  fairly  distinguishable  from  the  stages  immediately 
above  and  below,  may  be  called  a  Group  ;  *a  number  of  groups  sim- 
ilarly connected  and  distinguished,  forms  a  System  ;  and  an  assem- 
blage of  systems  forms  a  Series.  It  has  been  proposed  to  use  Era 
as  a  chronological  term  corresponding  with  Series,  Period  with 
System,  Epoch  with  Group,  and  Age  with  Stage. 

*  The  terminology  here  employed  differs  somewhat  from  that  proposed  by  the  members 
of  the  International  Geological  Congress  of  Bologna  (1881).  They  adopted  the  following 
order,  the  most  comprehensive  being  placed  first :  Group,  System,  Series,  Stage.  But, 
as  remarked  by  Sir  A.  Geikie  ("Text-book  of  Geology,"*p.  630,  ed.  2),  "it  may  be 
doubted  whether  the  recommendations  of  any  congress,  international  or  otherwise,  will 
be  powerful  enough  to  alter  the  established  usages  of  a  language.  The  term  Group  has 
been  so  universally  employed  in  English  literature  for  a  division  subordinate  in  value  to 
Series  and  System  that  the  attempt  to  alter  its  significance  would  introduce  far  more  con- 
fusion than  can  possibly  arise  from  its  retention  in  the  accustomed  sense."  To  this  it 
may  be  added  that  the  International  Geological  Congress  is  not  in  any  proper  sense 
a  representative  body,  and  in  science  the  principle  of  "  One  man,  one  vote,"  does  not  meet 
with  such  favor  as  it  does  in  some  political  circles. 


THE  ERAS  IN   GEOLOGICAL   HISTORY.  325 

Putting  aside  for  the  present  the  minor  divisions  into  groups  and 
stages,  we  may  restrict  ourselves  to  an  enumeration  of  the  systems 
and  series  which  are  at  present  in  general  use  among  the  geologists 
of  Great  Britain  and  in  many  other  parts  of  the  world,  so  far  as  local 
circumstances  permit.  For  convenience  of  inspection  they  are 
printed  in  a  tabular  form,  arranged  in  a  descending  order,  as  they 
might  occur  in  the  earth's  crust.  The  most  recent — the  beds  by 
which  the  list  is  begun — though  placed  as  on  the  table  for  the 
sake  of  symmetry,  are  hardly  of  sufficient  magnitude  to  deserve  the 
name  of  a  series,  possibly  not  even  of  a  system.  They  form  the 
concluding  chapter  in  the  earth's  history,  comparatively  brief,  but 
full  of  interest,  in  which  geology  joins  hands  with  archaeology,  and 
beyond  which,  so  far  as  we  at  present  know,  the  history  of  man 
does  not  extend.  In  regard  to  the  lowest  and  earliest — the  Archaean 
— we  have  not  attempted  to  separate  it  into  systems.  Divisions  of 
various  value  have  been  proposed,  groups  have  been  defined  and 
named  ;  but  in  the  general  absence  of  any  signs  of  life,  and  in  the 
exceptional  conditions  which  are  indicated  by  so  large  a  part  of  the 
rocks,  it  seems  unwise,  as  will  be  pointed  out  in  a  later  chapter,  to 
attempt,  with  our  present  imperfect  knowledge,  any  classification 
which  is  not  admittedly  provisional.  The  intermediate  systems  are 
mainly  distinguished  by  the  character  of  their  fossils.  They  are 
collected  into  three  great  "  series,"  which  by  the  older  geologists 
were  called  respectively  Primary,  Secondary,  and  Tertiary — the 
first,  second,  and  third  volumes  of  life's  history.  Afterward  the 
names  Palaeozoic,  Mesozoic,  and  Cainozoic  *  were  proposed,  and 
are  now  perhaps  more  frequently  used.  Palaeozoic  is  certainly 
commoner  than  Primary,  for  this  term  was  entangled  at  the  outset 
with  certain  hypotheses  which  were  proved  to  be  erroneous.  So 
Palaeozoic  was  preferred  and  Primary  avoided ;  for  words  may  ex- 
perience the  fate  of  men,  and  if  they  get  into  bad  company  when 
young  may  remain  for  long  under  a  cloud  and  be  viewed  askance 
by  respectable  folk.  This,  then,  is  the  list : 

Series.  System. 

Quaternary  or  Post-Tertiary       .       .       .       .    \  Recent  and  Prehistoric 

<  Pleistocene, 
j  Pliocene. 

Tertiary  or  Cainozoic       .       .  I  Miocene. 

Oligocene.  . 

[  Eocene. 

*  Meaning  Ancient-life  (time),  Intermediate-life  (time),  New-life  (time). 


326  THE   STORY  OF  OUR  PLANET. 

Series.  Systems. 

Cretaceous. 

Secondary  or  Mesozoic  .    J  Neocomian- 

^  Jurassic. 

Triassic. 
Permian. 
Carboniferous. 
Devonian. 


Primary  or  Palaeozoic        . 

Silurian. 

Ordovician. 
.  Cambrian. 
Archaean  or  Eozoic -    Systems  not  yet  distinguished. 

While  the  general  order  of  the  divisions  is  settled,  the  precise 
limits  of  the  systems  in  a  few  cases  are  still  matters  of  dispute.  For 
instance,  the  arrangement  which  has  been  followed  above  does  not 
correspond  in  all  respects  with  that  which  is  adopted  by  other 
writers.  The  following  are  the  principal  differences:  The  older 
authors  divided  the  Tertiary  into  three  systems — Eocene,  Miocene, 
and  Pliocene.  Oligocene,  which  is  composed  of  the  upper  part  of 
the  first  and  the  lower  half  of  the  second,  is  a  term  comparatively 
modern.*  In  the  Secondary  series  the  Cretaceous  and  the  Neocomian 
systems  are  called  respectively  the  Upper  and  Lower  Cretaceous. 
By  some  geologists  the  upper  part  of  the  Trias  is  made  a  separate 
system  under  the  name  of  Rhaetic.  In  favor  of  this  change  much 
may  be  said  ;  but,  as  the  system  is  poorly  represented  in  Britain, 
we  have  retained  the  more  familiar  arrangement.  Others  group  the 
Permian  with  the  Trias  under  the  name  of  New  Red  Sandstone,  or 
Poikilitic,  and  remove  the  former  into  the  Secondary  series.  The 
name  of  Old  Red  Sandstone  is  sometimes  used  instead  of  Devonian  ; 
as  will  be  seen  hereafter,  it  designates  only  a  local  and  exceptional 
deposit  of  that  period.  The  Ordovician  of  this  list  forms  part  of 
the  Silurian  of  the  Geological  Survey,  being  there  called  simply 
Lower  Silurian,  while  the  one  above  it  becomes  Upper  Silurian  ; 
while  other  geologists  include  the  Ordovician  in  the  Cambrian.  It 
may  suffice  at  present  to  call  attention  to  the  existence  of  these 
differences  of  opinion;  the  causes  of  them  will  be  more  conven- 
iently noticed  hereafter  in  connection  with  the  details  of  geological 
history. 

In  all  these  cases  the  reason  for  association  is  the  possession  of 

*  The  writer  is  not  quite  satisfied  as  to  the  necessity  of  the  distinction,  but  adopts  it 
in  deference  to  the  authority  of  geologists  who  have  made  the  Tertiary  deposits  a  special 
study. 


THE  ERAS  IN  GEOLOGICAL  HISTORY. 


3*7 


common  characteristics,  that  for  separation  the  existence  of  distinc- 
tions between  one  assemblage  and  another.  A  comparatively  slight 
change  in  the  fossils,  or  even  a  marked  change  in  lithological  char- 
acter, is  held  to  be  sufficient  in  parting  stage  from  stage,*  but  these 
must  become  more  conspicuous  in  the  case  of  groups,  and  so  on. 
Such  interruptions  when  well  marked  are  called  breaks ;  strati- 
graphical  breaks  when  there  is  found  to  be  either  a  very  marked 
alteration  in  the  mineral  character  of  a  large  group  of  rocks  or, 
better  still,  an  unconformity ;  f  or  palaeontological  when  one  fauna 
disappears  and  another  takes  its  place. 

It  must,  however,  be   remembered  that  these  breaks,  after  all, 


FIG.  124. — UNCONFORMITY  :   UPPER  OLD  RED  SANDSTONE  RESTING  ON  SILURIAN 
(VERTICAL),  NEAR  SICCAR  POINT,  BERWICKSHIRE. 

have  only  a  local  significance  and  value ;  an  unconformity  indicates 
that,  after  deposition  had  continued  for  a  certain  time,  erosion  took 
its  place,  to  give  way  again  to  the  former  process ;  but,  obviously, 
while  rock  was  being  destroyed  by  stream  or  wave  in  one  place  it 
was  being  deposited  in  another.  Neither  destruction  nor  deposition 
can  have  ever  been  universal. 

Again,  a  change  in  a  fauna  indicates,  not  a  general  destruction 
of  life  on  the  globe,  or  even  over  a  large  area  of  it,  but  simply  the 

*  The  term  zone  is  often  used  to  indicate  an  horizon  in  a  stage  at  which  a  particular 
fossil  or  an  exceptional  group  of  fossils  is  unusually  prevalent.  These  zones  are  often 
found  to  be  persistent  over  very  considerable  areas,  and  so  become  of  much  value  in 
correlation. 

f  When  the  base  of  one  formation  rests  on  different  parts  (sometimes  on  the  upturned 
edges)  of  the  beds  of  another  below  it,  this  is  called  unconformity  or  unconf amiability. 
When  the.  higher  beds  of  a  conformable  series  gradually  extend  beyond  the  lower  so  as 
to  indicate  an  enlarging  area  of  deposit,  they  are  said  to  overlap. 


328  THE   STORY  OF  OUR 

incoming  of  conditions  in  a  particular  district  which  caused  one 
fauna  either  to  migrate  or  to  dwindle  rather  rapidly,  and  to  be 
replaced  by  another  better  suited  to  the  altered  circumstances.  In 
some  cases  also  the  time  of  change  may  have  corresponded  with 
one  when  sediment  was  being  deposited  slowly,  so  that  the  interval 
may  have  been  really  a  long  one.  Thus  two  groups  or  systems, 
separated  in  one  place  by  a  sharply  defined  break,  stratigraphical 
and  palaeontological,  may  be  connected  in  another  by  a  considerable 
thickness  of  deposits,  in  which  the  replacement  of  one  fauna  by 
another  is  much  more  gradual.  For  instance,  in  England  the 
Eocene  system  is  separated  from  the  Cretaceous  by  a  fairly  well- 
marked  stratigraphical  and  a  very  strong  palaeontological  break  ;  but 
the  gap  in  some  parts  of  Europe  is  partially,  in  others  it  is  completely, 
filled  up,  and  the  Secondary  passes  into  the  Tertiary,  as  mediaeval 
into  modern  art.  Obviously,  then,  it  may  be  occasionally  very  diffi- 
cult to  decide  where  the  line  should  be  drawn,  not  only  between  the 
minor,  but  also  between  the  major  groupings.  In  such  case  some 
regard  is  paid  to  general  symmetry,  so  that  the  systems,  at  any  rate, 
shall  maintain,  as  far  as  may  be,  a  general  equality  in  chronological 
value,  and  not  be  representatives  of  periods  conspicuously  dispro- 
portionate in  length.  A  geological  classification  attempts  a  task 
similar  to  that  of  arranging  for  binding  the  numbers  of  a  periodical 
which  were  once  continuous,  but  are  now  seriously  tattered  and 
damaged.  The  great  thing  is  to  get  the  fragmentary  records  into  a 
correct  chronological  sequence,  and  then  to  do  the  best  possible  in 
order  to  make  the  volumes  approximately  of  the  same  thickness. 
At  any  rate,  a  bulky  tome  like  Liddell  and  Scott's  "  Lexicon  " 
should  not  stand  side  by  side  with  one  as  thin  as  a  quarto  copy  of 
the  Apocrypha. 

As  has  been  already  said,  all  the  stratified  rocks  must  have  been 
accumulated  within  a  certain  limited  time,  but  we  are  ignorant  as  to 
the  length  of  this.  We  are  not  in  a  very  much  better  position  if  we 
seek  to  obtain  an  idea  of  the  comparative  duration  of  the  Eras  or 
Periods.  The  only  scale  on  which  a  computation  could  be  founded 
would  be  that  of  the  thicknesses  of  the  several  rock  masses.  On  the 
assumption  that  the  measurements  were  accurate  and  a  fair  average 
could  be  obtained  by  making  allowance  for  coarseness,  fineness,  and 
the  like,  and  that  the  accumulation  of  each  kind  of  rock  had  been 
uniform  throughout  geological  history,  it  would  follow  that  the 
times  which  were  occupied  in  the  formation  of  these  several  rock 
masses  would  be  in  the  proportion  of  their  several  thicknesses.  This, 


THE  ERAS  IN  GEOLOGICAL   HISTORY.  329 

though  it  is  a  very  rough  method  of  obtaining  an  approximation,  is 
the  only  possible  one ;  for  we  are  so  ignorant  of  the  rate  at  which  a 
race  of  living  creatures  may  be  altered  by  the  stimulus  of  external 
changes  that  the  results  of  palaeontology  cannot  be  profitably 
utilized  at  present  for  purposes  of  chronological  comparison.  Still, 
inaccurate  as  any  results  must  be,  it  may  be  worth  while  to  consider 
for  a  moment  one  of  the  latest  estimates  which  have  been  made  ;  for 
by  this  method  alone  can  any  idea  be  obtained  of  the  relative 
durations  of  the  several  epochs  and  eras. 

The  estimate  given  by  Professor  Heilprin  omits  the  Quaternary 
or  post-Tertiary  rocks  as  inconsiderable,  for  probably  their  total 
thickness  would  fall  well  below  500  feet.  The  measurements, 
especially  in  the  more  modern  rocks,  represent  the  systems  as  they 
occur  in  America  rather  than  in  Europe,  where  the  Tertiary  deposits, 
at  any  rate,  are  apt  to  be  attenuated  or  fragmentary.  A  new  system, 
the  Laramie,  is  inserted  between  the  Eocene  and  the  Cretaceous, 
where  in  Britain  and  Western  Europe  generally  a  break  exists  of 
considerable  magnitude. 


„  Thickness 

Sy*te™'  infeet. 

Pliocene         .....  3,000 

Miocene     .....  4,000 

Oligocene       .....  8,000 

Eocene       .....  10,000 

Laramie          .....  4,000 

...         12,000 


... 
Neocomian  ) 

Jurassic         .....       6,000 


Thickness 
System*.  .„  ^ 

Triassic       .....  5,ooo 

Permian          .....  5,ooo 

Carboniferous     ....  26,000 

Devonian       .....  18,000 


Cretaceous  •  --,-,.,-   ,....-         33,ooc 


Cambrian      .....    21,000 
Archaean  .....         30,000 


This  estimate,  if  the  Laramie,  for  purposes  of  comparison,  be 
divided  equally  between  the  Secondary  and  the  Tertiary,  gives  for 
the  former  25,000  feet,  for  the  latter  27,000  feet,  with  106,000  feet 
for  the  Primary  or  Palaeozoic,  and  30,000  for  the  Archaean.  Re- 
ducing these  to  percentages,  we  have  Archaean  16,  Primary  56, 
Secondary  13.4,  and  Tertiary  14.6.  Little  confidence  can  be  felt, 
for  reasons  which  will  be  given  hereafter,  in  the  estimated  thickness 
of  the  Archaean,  but  the  remainder  are  probably  free  from  any  very 
serious  error  ;  so  the  above  table  indicates  that  the  Primary  strata 
are  just  double  the  Secondary  and  Tertiary  put  together,  and  are, 
roughly,  four  times  each  of  them.  Supposing,  then,  that  these  strata 
were  accumulated  at  an  approximately  uniform  rate  (and  there  is 
nothing  to  prove  that  this  was  quicker  in  Primary  times),  the  dura- 


33°  THE   STORY  OF  OUR  PLANET. 

tion  of  the  eras  over  which  these  three  great  divisions  of  the  earth's 
life  history  extended  would  correspond  approximately  with  the 
numbers  560,  134,  and  146. 

By  means  of  the  comparison  of  fossils  from  widely  separated 
localities,  and  a  study  of  the  succession  of  the  various  forms  of  life 
in  the  different  parts  of  the  globe,  formation  has  been  connected 
with  formation  and  place  with  place.  Thus  it  has  been  discovered 
that  the  earth  was  not  occupied  in  past  times,  any  more  than  now, 
by  the  same  fauna  in  all  its  parts,  but  that  even  then  representa- 
tive species  and  genera  existed,  together  with  other  differences 
indicating  the  effects  of  geographical  limits  and  climatal  conditions. 
Still,  notwithstanding  this,  the  fauna  or  flora  of  a  particular  system 
is  so  far  marked  out  by  common  characteristics  that  an  experienced 
palaeontologist,  on  comparing  a  parcel  of  fossils  from  South  Africa 
or  Australia  with  those  found  in  a  certain  system  in  Europe,  cannot 
fail  to  be  struck  by  the  resemblance  between  the  two.  He  also 
finds,  on  further  inquiry,  that  the  correspondences  are  exhibited  by 
the  contents  of  groups  of  strata  which  follow  the  same  order  of 
succession  as  they  do  in  his  own  country.  Suppose,  for  instance, 
one  bed  reminds  him.  of  the  Silurian,  another  of  the  Devonian,  and 
a  third  of  the  Carboniferous  of  Europe,  these  beds  will  come  in  the 
same  sequence  in  the  opposite  hemisphere  of  the  globe.  Accord- 
ingly, these  terms  are  in  use  even  at  the  antipodes  of  the  places 
where  they  originated,  and  the  epochs  which  they  represent  have 
been  supposed  to  correspond,  roughly  speaking,  in  time. 

But  this  notion  of  geological  contemporaneity  from  the  general 
similarity  of  fossils  must  not  be  pressed  too  far.*  Professor  Huxley, 
who  has  dealt  with  this  subject  in  his  usual  masterly  style,  has 
pointed  out  that  the  results  of  the  study  of  fossils  might  be  formu- 
lated in  two  laws  "  of  inestimable  importance ;  the  first,  that  one 
and  the  same  area  of  the  earth's  surface  has  been  successively 
occupied  by  very  different  kinds  of  living  beings  ;  the  second,  that 
the  order  of  succession  established  in  one  locality  holds  good 
approximately  in  all.  The  first  of  these  laws,"  he  says,  "  is  universal 
and  irreversible  ;  the  second  is  an  induction  from  a  vast  number  of 
observations,  though  it  may  possibly,  and  even  probably,  have  to 
admit  of  exceptions.  As  a  consequence  of  the  second  law,  it  follows 
that  a  particular  relation  frequently  subsists  between  a  series  of 
strata  containing  organic  remains  in  different  localities.  The  series 

*  "  Lay  Sermons,  Addresses,  and  Reviews,  No.  X.  (Geological  Contemporaneity)." 


THE  ERAS  IN  GEOLOGICAL  HISTORY.  tft 

resemble  one  another,  not  only  in  virtue  of  a  general  resemblance 
of  the  organic  remains  in  the  two,  but  also  in  virtue  of  a  resemblance 
in  the  order  and  character  of  the  serial  succession  in  each."  Thus  a 
correspondence  in  succession,  as  he  says,  "  came  to  be  looked  upon 
as  a  correspondence  in  age  or  contemporaneity."  But  it  is  relative 
rather  than  absolute  contemporaneity. 

At  the  present  time  we  find  that  the  range  of  a  species,  and  to 
some  extent  even  that  of  a  genus,  is  limited  by  geographical  bar- 
riers and  climatal  conditions.  The  further  spread  of  this  organism 
is  prohibited  by  ocean  depths,  of  that  by  mountain  barriers  or  by 
desert  plains  ;  in  one  direction  the  invaders  are  repelled  by  heat,  in 
another  by  cold.  "  Thus  far  shalt  thou  go,  and  no  farther,"  is  a 
command  common  enough  in  the  realm  of  Nature. 

Accordingly  it  is  doubtful  whether  similar  floras  and  faunas  could 
have  been  strictly  contemporaneous  in  regions  far  apart,  and  under 
very  different  climatal  conditions.  Whatever  may  be  the  history  of 
the  actual  origin  of  a  species,  this  at  least  seems  clear — that,  if  it 
has  a  wide  geographical  range,  this  must  be  a  consequence  of  migra- 
tion. Accordingly  it  could  hardly  begin,  and  probably  would  not 
end,  its  term  of  existence  simultaneously  in  two  places  very  far  sep- 
arated— as,  for  instance,  on  the  same  circle  of  longitude,  but  on 
opposite  sides  of  the  equator.  It  is  still  more  improbable  that  a 
flora  or  fauna  which  has  been  discovered  in  some  district  within  the 
tropics  should  be  contemporaneous  with  a  similar  one  in  temperate 
regions.  Any  assemblage  of  organisms  indicates  a  certain  environ- 
ment, and  among  its  factors  climate  is  not  the  least  important ;  but 
it  is  almost  impossible  that  the  corresponding  conditions  of  exist- 
ence should  have  been  coincident  in  regions  separated  by  many 
degrees  of  latitude.  Much  more  probable  is  it  that  the  two  epochs 
thus  indicated  were  in  a  sequence,  that  either  the  denizens  of  the 
temperate  zones  were  driven  by  an  increased  cold  toward  the  equa- 
tor, or  a  migration  in  the  opposite  direction  was  produced  by  an 
increase  of  heat.  As  changes  of  climate  and  the  consequent  dis- 
placement of  living  creatures,  so  far  as  we  know,  are  brought  about 
slowly,  any  real  contemporaneity  becomes  almost  impossible  in 
such  a  case  as  this.  So  far,  then,  as  a  conclusion  is  possible  in 
regard  to  this  matter  it  may  be  thus  expressed  :  A  correspondence 
of  flora  and  fauna  may  be  indicative  of  a  general  contemporaneity 
in  places  which  differ  considerably  in  longitude,  but  only  slightly  in 
latitude,  while  it  has  the  contrary  significance  if  the  agreement  is 
in  longitude,  and  the  separation  in  latitude  is  very  marked. 


33 2  TffE  STOKY  OF  OUR  PLANET. 

But  inasmuch  as  the  second  of  the  laws  enunciated  by  Professor 
Huxley — that  of  the  persistence  of  the  order  of  succession — holds 
good  generally,  if  not  absolutely,  in  all  parts  of  the  earth :  as  chap- 
ter follows  chapter  in  the  same  sequence  in  the  records  of  the  rocks, 
and  in  the  story  of  the  development  of  life  :  the  names  which  have 
been  adopted  for  one  region  may  be  conveniently  applied  to  another, 
provided  it  be  understood  that  a  definite  position  in  a  series,  rather 
than  a  real  contemporaneity,  is  implied  by  their  use.  The  latter, 
under  certain  circumstances,  may  also  exist,  though  here  the  unit 
of  measurement  must  be  centuries  rather  than  years,  but  under 
others  the  difference  may  be  large,  as  we  count  time.  Still,  in  most 
cases,  the  two  groups  or  systems  are  not  likely  to  be  parted  by  a 
wide  geological  interval.  They  will  be  related,  so  to  say,  as  are  the 
men  of  successive  generations  rather  than  of  successive  eras.  For 
this  correspondence  of  the  floras  and  faunas  of  two  or  more  sep- 
arated groups  of  rocks,  Professor  Huxley  has  proposed  the  term 
"  homotaxis"*  in  order  to  express  a  correspondence  of  position  with- 
out predicating  a  contemporaneity  of  time.  It  is  the  former  rather 
than  the  latter  sense  which  must  be  understood  in  the  following 
chapters  when  reference  is  made  to  the  life  history  of  the  earth  dur- 
ing any  geological  period  or  epoch. 

But  in  any  attempt  to  depict,  even  in  the  broadest  outlines,  the  past 
life  history  of  the  globe,  and  to  speculate  on  the  development  of 
successive  floras  and  faunas,  the  inherent  imperfection  of  the 
geological  record  must  never  be  forgotten.  It  is  now  a  quarter  of 
a  century  since  Darwin  wrote  that  well-known  chapter  in  his  classic 
work  on  the  "Origin  of  Species,"  and  though  since  that  time  the 
labor  of  numerous  indefatigable  writers  has  filled  many  a  gap  and 
supplied  many  a  link  for  which  he  had  vainly  sought,  yet  even  now 
the  lacunae  are  very  great,  and  the  materials  at  the  disposal  of 
geologists  can  never  be  anything  but  fragmentary. 

These  inevitable  imperfections  arise  from  various  causes,  which 
may  be  summarized  under  two  heads — the  one  relating  to  the 
restrictions  which  nature  has  imposed  upon  our  investigations,  the 
other  to  the  inherent  defects  of  the  record  itself.  As  regards  the 
former,  we  are  practically  precluded  from  examining  more  than  a 
very  small  portion  of  the  earth's  surface.  It  has  been  already 
stated  that  something  over  seven-tenths  of  the  globe  is  covered  by 
sea.  Here,  then,  the  dredge  may  bring  up  samples  of  the  mud  or 

*  It  signifies  "  the  same  order." 


THE  ERAS  iff  GEOLOGICAL   HISTORY.  333 

ooze  now  in  process  of  deposition,  but  of  the  underlying  strata  we 
can  obtain  no  information.  Again,  a  great  portion  of  the  land 
itself  is  hardly  less  inaccessible.  Lakes,  rivers,  snowfields,  glaciers, 
conceal  anything  beneath  them  as  effectually  as  the  waters  of  the 
ocean  ;  large  tracts  also  are  so  covered  up  by  sands,  marshes,  and 
alluvial  deposits  as  to  be  practically  out  of  reach.  Probably  not 
more  than  one-fifth  of  the  earth's  surface  by  any  possibility  can 
ever  be  examined,  and  of  that  at  the  present  time  very  large  tracts 
are  still  unexplored.  Little  or  nothing  is  known  of  the  geology  of 
considerable  areas  in  Australia  and  the  two  Americas,  and  of  still 
larger  districts  in  Central  Asia  and  Africa.  But  even  in  those 
regions  where  the  palaeontologist  has  done  his  best  the  opportuni. 
ties  of  obtaining  materials  for  purposes  of  study  are  very  limited. 
He  is  restricted  to  what  can  be  learnt  from  the  outcropping  edges 
of  beds,  from  the  natural  sections  afforded  by  ravines,  or  from 
artificial  excavations  in  quarries,  mines,  and  cuttings.  Yet  how 
small  a  part  of  any  one  stratum  is  thus  subjected  to  examination 
compared  with  its  volume  as  a  whole  !  "  We  are  very  much  in  the 
position  of  persons  called  upon  to  describe  the  cloth  in  a  warehouse 
in  which  they  are  only  allowed  to  finger  the  edges  of  a  few  bales. 
We  can  reason  upon  what  we  do  find,  but  must  be  very  cautious  in 
forming  theories  about  what  we  do  not  find."* 

Next  in  regard  to  the  imperfections  inherent  in  the  record  itself. 
The  bodies  of  many  animals  are  destitute  of  hard  parts — such  as 
shell  or  bone;  that  of  a  "jellyfish  "or  a  "  sea  anemone  "  will  be 
quickly  disintegrated  after  death,  and  it  is  by  the  rarest  chance 
that  any  trace,  however  faint,  of  such  a  creature  remains.  Again, 
any  animals  strictly  terrestrial  in  their  habits  can  only  be  preserved 
under  exceptional  conditions.  There  are  in  several  parts  of  Eng- 
land moors  which  never  have  been  touched  either  by  plow  or 
spade.  If  a  pit  be  dug,  it  gives  an  opportunity  of  examining  the 
soil  which  has  been  virgin  for  myriads  of  years — since  last  the  land 
arose  from  the  sea,  whenever  that  may  have  been.  Take  such  a 
moor  as  Cannock  Chase,  in  Staffordshire ;  it  is  now  overgrown  with 
brake  and  gorse,  heather  and  heath,  whortleberry,  crowberry,  and 
other  moorland  plants.  Here  and  there  is  a  solitary  thorn  or  oak, 
or  a  cluster  of  birch.  Insects  flutter  over  the  plants,  birds  flit  from 
bush  to  bush,  the  hawk  circles  overhead,  grouse  and  black-cock  are 
still  flushed  on  the  hillside,  the  rabbit  darts  among  the  fern,  and 
the  fox  skulks  through  the  gorse.  In  olden  time,  when  men  were 

.     *The  author,  "  Geology"  (Manuals  of  Elementary  Science). 


334  THE   STORY  OF  OUR  PLANET. 

fewer  and  collieries  unknown,  the  wild  creatures  were  far  more 
plentiful  than  now,  yet  what  record  can  be  found  of  all  these 
countless  generations  of  plants  and  animals  ?  The  soil,  as  a  rule,  is 
a  little  discolored  by  traces  of  decayed  vegetable  matter,  generally 
past  identification,  and  that  is  all.  The  tree  that  dies  on  such  a 
moorland  drops  piecemeal  to  the  ground  ;  there  it  lies,  wetted  by  the 
rain  and  dried  by  the  sun,  till  at  last  it  turns  to  touchwood  and  then 
to  dust.  The  smaller  plant  more  quickly  suffers  the  same  fate;  so 
too  the  animal  which  dies  and  lies  unburied  upon  the  surface,  till 
its  bleaching  bones  pass  also  into  dust  and  are  "  blown  about  the 
desert  hills."  The  moors  till  late  years  abounded  in  game  ;  herds  of 
red  deer  almost  certainly  roamed  over  them  centuries  before  the 
fallow  deer,  which  still  linger,  vere  introduced.  They  and  other 
creatures,  bigger,  and  now  extinct,  have,  like  an  "  insubstantial 
pageant,  faded,""  and  left  "  not  a  rack  behind."  Terrestrial  animals, 
and  to  no  small  extent  land  plants  also,  can  only  be  preserved  under 
exceptional  circumstances.  If  they  are  mired  in  marshes,  engulfed 
in  chasms,  drowned  in  rivers,  swept  away  by  floods,  then  their 
remains  have  a  chance  of  being  inclosed  in  some  protective  cover- 
ing and  handed  down  to  future  ages  ;  but  the  creature  that  lies 
down  to  die  upon  the  moorland  is  resolved  into  impalpable  gases 
and  formless  dust. 

But  the  possibilities  of  imperfection  in  the  geological  record  are 
not  even  yet  exhausted.  Many  fossil  remains,  which  for  a  time  have 
been  successfully  preserved,  may  be  afterward  destroyed.  Heat, 
often  due  to  the  intrusion  of  igneous  rocks,  may  cause  great  chem- 
ical changes,  and  obliterate  all  traces  of  fossils.  Water,  as  it  per- 
colates through  the  more  porous  strata,  may  attack  the  mineral  salts 
in  shell  or  bone,  and  remove  them  entirely.  A  mass  of  sandstone 
commonly  proves  a  barren  hunting  ground  for  the  palaeontologist, 
and  the  reason,  no  doubt,  in  many  cases  is  that  which  has  been 
just  given.  Again,  large  masses  of  rock  have  been  swept  away  by 
denudation,  and  their  organic  contents  have  been  ground  into  powder. 

So,  on  a  review  of  the  whole  subject,  we  see  that  the  utmost 
caution  is  requisite  in  this  department  of  geological  speculation. 
Making  allowance  for  the  fact  that  at  best  we  can  only  deal  with 
the  hard  parts  of  animals,  the  palaeontologist  arrives  at  his  infer- 
ences as  to  the  history  of  the  past.  But  it  must  never  be  forgotten 
that  one  grain  of  positive  evidence  is  more  valuable  than  tons  of 
negative  evidence ;  the  latter  is  only  useful  in  suggesting  caution, 
the  former  supplies  the  materials  for  actual  advance. 


CHAPTER   III. 

THE    ARCHAEAN   ERA. 

THE  Archaean  series  contains  rocks  of  very  different  types.  The 
majority  are  in  a  crystalline  condition,  but  some  are  sedimentary 
deposits,  practically  unaltered.  These  represent  the  two  extremes, 
but  intermediate  forms  occur  which  link  them  together;  in  other 
words,  not  only  sedimentary  rocks  can  be  found  in  which  crystalline 
minerals  are  beginning  to  make  their  appearance,  and  thus  to  ob- 
scure the  original  fragmental  structure,  but  also  schists,  which, 
though  they  are  now  thoroughly  crystalline,  indicate,  by  their  com- 
position and  mutual  relations,  that  they  must  have  begun  their  his- 
tory as  sediments.  Of  the  two  extreme  types  the  former,  or  crystal- 
line one,  is  a  group  of  rocks  the  origin  of  which,  as  will  presently  be 
indicated,  is  a  matter  of  great  uncertainty  ;  the  latter  differs  but 
little  from  the  oldest  members  of  the  Primary  or  Palaeozoic  series. 
It  must  never  be  forgotten  that  the  division  between  those  and  the 
newest  members  of  the  Archaean  series  has  the  same  significance 
(but  no  more)  as  that  which  separates  the  Primary  from  the  Second- 
ary, or  the  Secondary  from  the  Tertiary.  If  we  slip  unconsciously 
into  the  habit  of  assuming  that,  instead  of  a  gradual  change  from 
the  one  era  to  the  other,  there  is  a  great  gulf  fixed  between  them, 
we  shall  be  quickly  entangled  in  difficulties,  with  the  satisfaction  of 
knowing  that  they  are  of  our  own  creation.  So  the  break  here,  as 
in  other  cases,  is  a  question  of  convenience,  subject,  of  course,  to 
the  principles  generally  adopted  in  classification.*  In  some  parts  of 
this  country,  and  of  others,  a  zone  of  fossils — very  few  indeed  in 
number,  but  distinctive  in  character — happens  to  occur  immediately 
above  some  beds  with  well-marked  lithological  features,  beneath 
which  only  obscure  traces  of  life  have  been  found ;  and  thus  the 
latter  form  a  good  base  to  the  Cambrian  system,  and  introduce  the 
Primary  or  Palaeozoic  series.  This  stage  is  generally  separated  by 
an  unconformity  from  the  beds  below.  These  sometimes  do  not 
appeal  to  be  very  much  more  ancient  than  it ;  indeed,  occasionally, 

*  See  p.  328. 

335 


336  THE   STORY  OF  OUR  PLANET. 

when  the  above-named  zone  of  fossils  cannot  be  found,  geologists 
differ  as  to  the  exact  spot  where  the  line  of  separation  should  be 
drawn,  but  in  other  cases  the  unconformity  is  most  strongly  marked, 
and  the  rocks  underlying  it  are  in  a  very  different  mineral  condition, 
so  that  it  obviously  indicates  a  very  long  interval  of  time.  In  the 
Archaean,  as  already  stated,  only  obscure  traces  of  life  have  been 
found,  still  there  are  indubitable  traces,  and  a  study  of  the  fauna  of 
the  Cambrian  system  leads  to  the  conviction  that  it  does  not  repre- 
sent the  first  beginning  of  life,  but  that  its  denizens  must  have  had  a 
long  train  of  predecessors.  So,  though  at  present  we  can  hardly 
venture  to  use  such  a  phrase  as  "  the  Archaean  fauna,"  the  next 
five-and-twenty  years  may  see  this  rendered  definite  and  augmented, 
as  has  been  the  case  with  the  fauna  of  the  lowest  part  of  the  Cam- 
brian* during  the  past  quarter  of  a  century.  If  so,  geologists  must 
either  cease  to  regard  the  Archaean  as  an  Azoic  group  of  rocks,  f  or 
augment  the  Palaeozoic  series  by  enlarging  the  Cambrian,  or  by 
adding  a  new  system.  The  rocks  of  the  Archaean  series  present 
many  special  characteristics  ;  that  era  was  the  starting  point  of  the 
earth's  history,  in  regard  not  only  to  the  development  of  life,  but 
also  to  the  deposition  of  rocks.  If  ever  conditions  prevailed  on 
this  globe  which  were  markedly  different  from  those  of  the  present 
age,  or  of  later  geological  history,  this  must  have  been  during  the 
Archaean  era.  For  these  reasons  we  purpose  to  treat  it  separately 
from  the  rest,  as  forming  a  kind  of  introductory  chapter  to  the 
history  of  the  development  of  the  earth's  surface  and  of  its  inhab- 
itants. 

In  many  parts  of  Ross-shire — as,  for  instance,  in  the  neighbor- 
hood of  Loch  Maree — the  lowest  rocks  visible  are  rather  coarsely 
crystalline  schists  and  gneisses,  in  some  cases  differing  little  from 
granite  or  other  rocks  of  igneous  origin.  Still,  as  a  rule,  they  are 
distinguished  by  a  certain  tendency  to  a  banded  or  a  foliated  struc- 
ture, and  so  depart  rather  distinctly  from  the  normal  types  of  igne- 
ous rocks.  When  the  gneisses  are  traced  for  considerable  distances 
over  the  country,  they  are  found  to  become  yet  more  variable  in 
character,  and  to  be  associated — whether  by  a  gradual  transition  or 

*  The  most  important  discoveries  were  made  by  Dr.  H.  Hicks,  and  announced  in  a 
paper  by  himself  and  the  late  Professor  Harkness  in  the  Quarterly  Journal  of  the  Geo- 
logical Society,  vol.  xxvii.  (1876),  p.  384. 

•f-The  term  Azoic  (lifeless)  has  been  employed  to  designate  the  Archaean.  Others  have 
called  it  Eozoic  (dawn  of  life).  Perhaps,  on  the  whole,  Archaean  (ancient),  proposed  in 
1874  by  Professor  J.  D.  Dana,  is  better,  as  it  expresses  a  simple  fact. 


THE  ARCH  A?  AN  ERA. 


337 


by  a  rather  sudden  change  is  not  yet  determined — with  various 
quartzose,  or  micaceous,  or  calcareous  schists,  sometimes  even  with 
marbles.  Thus,  whatever  may  have  been  the  origin  of  the  more 
granitic  members  of  this  assemblage,  we  can  hardly  doubt  that  the 
last  mentioned  were  formerly  sediments,  and  that  their  present  crystal- 
line condition  has  been  subsequently  assumed.  These  rocks  have 
been  variously  called  Fundamental,  Lewisian,  and  Hebridean 
gneisses.  For  many  a  mile'  on  either  side  of  Loch  Maree  they  are 


FIG.  125. — LOCH  MAREE — AMONG  THE  "  FOUNDATION  STONES  "  OF  SCOTLAND. 


overlain  by  a  huge  mass  of  ruddy  grit,  often  two  or  three  thousand 
feet,  and  sometimes  more,  in  thickness,  called  the  Torridon  Sand- 
stone. It  is  very  largely  composed  of  grains  of  quartz  and  felspar, 
and  has  been  so  little  changed  that  no  doubt  can  exist  as  to  its 
nature  and  origin.  These  grains  obviously  have  been  obtained  from 
rocks  identical  with  those  now  underlying  the  grit,  the  base  of  which 
is  often  a  conglomerate  or  breccia  composed  of  fair-sized  fragments 
of  gneiss  and  schists.  The  section,  then,  proves  beyond  all  question 
that,  whatever  may  have  been  the  history  of  the  Hebridean  rocks, 
they  had  assumed  their  present  condition,  mineral  and  structural, 
before  the  Torridon  Sandstone  began  to  be  formed.  On  the  latter 
rock  rests  a  quartzite  ;  between  the  two  another  unconformity  inter- 


338 


THE    STORY  OF  OUR  PLANET. 


venes,  which,  however,  probably  does  not  represent  a  very  long 
period  of  time.  The  quartzite  clearly  was  once  a  sandstone,  and  in 
parts  of  it  tubular  markings  may  be  found,  which  were,  no  doubt, 
made  by  marine  worms.  The  age  of  this  rock  can  now  be  fixed  with 
precision.  About  three  years  since  the  geological  surveyors*  found 


FIG.  126. — BEN  SLIOCH — A  MOUNTAIN  OF  TORRIDON  SANDSTONE. 

fossils  in  some  shaly  beds  just  at  the  top  of  this  quartzite  Avhich 
proved  the  latter  to  be  at  the  very  base  of  the  Cambrian.  Thus 
even  the  Torridon  Sandstone  must  be  included  in  the  Archaean,  and 
the  gneissoid  rocks  obviously  belong  to  a  much  earlier  part  of  the 
series. 

In  North  America  an  enormous  series  of  crystalline  rocks  exists, 
some  of  which  bear  a  close  resemblance  to  the  gneisses  and  other 

*  The  discovery  was  described  in  a  paper  read  by  the  Director-General  of  the  Geological 
Survey  at  the  Cardiff  meeting  of  the  British  Association.  Geological  Magazine,  1891, 
p.  498. 


THE  ARCffsEAlV  ERA.  339 

coarse  crystalline  schists  of  the  Northwest  Highlands.*  The  rocks 
cover  a  vast  area,  extending  northward  from  the  left  bank  of  the  St. 
Lawrence  River — from  which  they  were  called  Laurentian — to  the 
Arctic  Ocean,  an  area  probably  of  about  200,000  square  miles.  They 
are  overlain  in  places  by  a  variable  system  of  rocks,  which  are  com- 
paratively unaltered,  and  sometimes  contain  fragments  of  the  older 
series  ;  to  this  the  late  Sir  W.  Logan  gave  the  name  of  Huronian. 
In  many  places  the  latter  are  in  turn  covered  unconformably  by 
strata  which  are  proved  by  their  fossil  contents  to  be  of  Cambrian 
age,  and  the  Huronian  rocks  are  now  generally  supposed,  like  the 
Torridon  Sandstone,  to  belong  to  the  latest  part  of  the  Archaean 
series.  Rocks  similar  to  the  Laurentians  crop  up  in  several  other 
parts  of  North  America,  though  never  on  so  grand  a  scale,  so  that 
in  this  continent  the  Archaean  series  is  well  represented.  Its  rocks, 
as  already  intimated,  exhibit  considerable  differences  in  mineral  and 
structural  character.  Sir  W.  Logan,  who  was  the  first  to  describe 
them  in  any  detail,  grouped  them  under  two  broad  divisions,  calling 
the  assemblage  of  highly  crystalline  rocks  Laurentian,  and  those 
which  were  obviously  fragmental  Huronian.  Rocks  of  igneous 
origin,  for  the  most  part  intrusive,  are  present  in  both  these  divi- 
sions ;  but,  putting  them  aside,  the  older  consist  of  a  very  thick 
mass  of  gneisses  and  highly  crystalline  schists — quartzose,  micaceous, 
and  hornblendic — with  occasionally  some  marbles.  In  the  lower 
part  gneissoid  rocks  predominate,  of  which  the  upper  exhibit  greater 
variety,  and  are,  on  the  whole,  less  coarsely  crystalline.  The  total 
thickness  was  supposed  to  be  about  30,000  feet.  Sir  W.  Logan 
divided  this  mass  for  purposes  of  convenience  into  two  parts — a 
Lower  and  an  Upper  Laurentian.  Subsequently  it  was  proposed  to 
sever  the  latter  from  the  Laurentian  and  call  it  the  Norian  system. 
The  distinction  to  a  great  extent  was  founded  on  a  grave  error,  for 
the  rock  which  was  regarded  as  characteristic  of  this  Norian  system, 
and  held  to  be  metamorphic,  is  both  igneous  and  intrusive,  so  that, 
as  its  date  is  uncertain,  it  is  of  no  use  in  a  chronological  classification. 
Hence,  as  no  real  demarcation  has  been  as  yet  established,  science 
is  not  a  gainer  by  the  name.  One  or  two  other  subdivisions  have 
been  proposed ;  but  as  their  value  was  never  better  than  doubtful, 
they  need  not  be  included  in  this  volume. 

Crystalline  schists  and  gneisses  occur  in  many  other  parts  of  the 


*  There   can   be  no   doubt  that   they  are    also    largely   represented  in  the   Central 
Highlands. 


34°  THE   STORY  OF  OUR  PLANET. 

world,  which  are  provisionally  referred  to  the  Archaean  series.  In 
some  cases  these  can  be  proved  to  be  earlier  than  the  Cambrian 
period,  in  others  only  to  be  much  more  ancient  than  the  oldest 
rocks  which  rest  upon  them.  The  latter  in  one  place  may  belong 
to  the  Tertiary  series,  in  another  to  the  Secondary,  in  a  third  to  the 
Primary.  For  instance,  the  crystalline  schists  and  gneisses  of  the 
Alps  are  overlain — here  by  Jurassic  or  Triassic  strata,  there  by 
Carboniferous,  there  by  Silurian.  From  one  end  of  the  chain  to 
the  other  they  have  characteristics  in  common,  so  that  they  may  be 
regarded  with  good  reason  as  an  inseparable  whole.  They  present 
the  closest  possible  resemblance  in  all  essential  points  to  rocks 
which,  in  other  places,  are  unquestionably  older  than  the  Cambrian 
period.  Hence  it  seems  probable  that  they  too  are  Archaean.  In 
cases  of  which  this  one  is  a  type  the  age  is  a  matter  of  inference,  for 
it  can  only  be  proved  that  the  rocks  are  very  old  ;  in  those  pre- 
viously mentioned  it  is  a  certainty.  A  correspondence  in  age  is 
inferred  from  a  correspondence  in  the  general  characters,  more 
especially  in  regard  to  those  which  are  likely  to  be  related  to  the 
history  of  the  rock ;  so  that  at  the  present  day  many  geologists 
(among  whom  the  writer  must  be  counted)  would  go  so  far  as  to  say 
that  if  a  mass  of  schists  be  found«*vhich  appear,  in  the  main,  to  have 
been  formerly  sediment,  but  are  now  in  a  thoroughly  crystalline 
condition,  the  probability  that  they  are  Archaean  is  so  strong  that 
they  may  be  with  safety  placed,  at  any  rate  provisionally,  in  that 
series,  unless  some  cause  can  be  shown  to  the  contrary. 

The  reasons  which  have  led  to  this  conclusion  are  too  technical  to 
be  discussed  in  a  work  like  the  present ;  but  an  idea  of  their  nature 
.and  of  the  general  character  of  the  controversy  (which  is  almost  as 
old  as  geology)  may  be  indicated  in  some  words  written  by  the 
author  in  1892.*  "When  the  geologist  has  learnt  from  the  micro- 
scope to  recognize  differences  of  structure  in  crystalline  rocks  and  to 
appreciate  their  significance,  he  finds  that  a  wider  problem  is  pre- 
sented to  his  mind,  provided  that  he  has  not  been  led  by  the 
fascinations  of  laboratory  studies  to  despise  or  neglect  work  in  the 
field.  Granted  that  one  group  of  rocks,  covered  by  the  term  meta- 
morphic,  has  undergone  great  changes  since  its  members  were  first 
deposited  or  solidified,  can  these  be  connected  with  any  phase  in  the 
earth's  history  ?  have  they  any  chronological  significance  ?  Even 

*"The   Microscope's   Contributions    to  the   Earth's   Physical    History"   (The   Rede 
Lecture  to  the  University  of  Cambridge,  1892.     See  Nature,  xlvi.  p.  180). 


THE  ARCHAEAN  ERA.  341 

twenty  years  since  few  geologists  would  have  hesitated  to  reply, 
'  None  whatever  :  a  rock  may  have  undergone  metamorphism  at 
any  epoch  in  the  past.  Muds  and  sands  of  Eocene,  Jurassic,  Car- 
boniferous, Silurian,  of  any  geological  age,  have  been  converted  into 
crystalline  schists.  Proofs  of  some  part  of  this  assertion  can  be 
found  even  within  the  limits  of  the  British  Isles  ;  it  can  be  com- 
pletely established  within  those  of  Europe.'  But  during  the  last 
few  years  this  hypothesis  has  been  on  its  trial ;  witness  after  witness 
in  its  favor  has  been,  so  to  say,  brought  into  court,  and  has  broken 
down  under  cross-examination.*  I  can  assert  this  without  hesita- 
tion, for  I  have  some  personal  knowledge  of  every  notable  instance 
in  Europe  which  has  been  quoted  in  the  debate.  Microscopic  study, 
combined  with  field  work,  has  invariably  discovered  that  some  very 
important  link  in  the  supposed  chain  of  proof  is  wanting,  and  has 
demonstrated,  without  exception,  that  these  crystalline  schists  are 
very  old,  much  more  ancient  always  than  any  neighboring  rock  to 
which  a  date  can  be  assigned.  .  .  It  has  been  also  demonstrated 
that  sedimentary  masses,  after  they  have  been  buried  deep  beneath 
superimposed  strata  and  exposed  to  great  pressure,  have  emerged 
comparatively  unchanged.  Such  rocks  are  most  valuable  as  illustra- 
tions of  the  effects  of  dynamical  and  other  agencies  ;  but  they  are 
sufficiently  distinct  from  the  crystalline  schists  to  indicate  that  the 
environment  in  the  one  case  must  have  differed  greatly  from  that  in 
the  other.  The  results  of  contact-metamorphism  prove  that  heat  is 
an  important  agent  of  change ;  but  as  these  also  present  their  own 
marked  differences,  they  fail  to  afford  a  complete  solution  of  the 
problem. 

"  Moreover,  among  ordinary  sedimentary  rocks  we  cannot  fail  to 
notice  that,  as  a  rule,  the  older  the  rock  the  greater  the  amount  of 
mineral  change  in  its  constituents.  A  good  illustration  of  this  is 
afforded  by  the  Huronian  system  of  North  America,  the  rocks  of 

*  A  single  instance  may  suffice  to  indicate  the  reckless  way  in  which  statements  of  this 
kind  have  been  made.  At  the  meeting  of  the  Geological  Congress  in  London  in  1888 
it  was  asserted  that  in  some  parts  of  the  Alps  belemnites  occur  together  with  garnets  and 
staurolites  in  certain  nearly  crystalline  schists,  on  which  ground  it  was  maintained  that  cer- 
tain other  schists  which  contain  the  same  minerals  are  altered  rocks  of  Jurassic  age,  in 
which  metamorphism  has  been  more  extreme.  The  following  are  the  facts  of  the  case  : 
Some  of  the  rocks  in  the  group,  of  which  the  latter  schists  unquestionably  are  members,  are 
found  as  fragments  in  a  rock  which  all  geologists  agree  in  recognizing  as  Trias  (I.  e. ,  older 
than  the  Jurassic  system).  The  rock  which  contains  the  belemnites  has  not  undergone  any 
important  amount  of  alteration,  and  the  minerals  in  it  are  neither  garnets  nor  staurolites, 
but  certain  hydrous  silicates,  the  occurrence  of  which  has  no  significance.  In  a  word, 
a  most  important  generalization  is  founded  on  a  mistaken  identification  of  minerals. 


342  THE   STORY  OF  OUR  PLANET. 

which  are  rather  older  than  the  Cambrian  of  this  country.  Some 
of  them,  while  still  retaining  distinct  indications  of  a  sedimentary 
origin,  have  become  partly  crystalline,  and  supply  examples  of  a 
transition  from  a  normal  sediment  to  a  true  crystalline  schist.  Even 
the  older  Palaeozoic  rocks  almost  invariably  exhibit  considerable 
mineral  changes,  though  with  them  it  is  only  on  a  microscopic  scale. 
Hence,  taking  account  of  all  these  results,  we  seem  to  be  forced  to 
the  conclusion  that  the  environment  necessary  for  changing  an 
ordinary  sediment  into  a  crystalline  schist  existed  generally  only  in 
the  earliest  ages,  and  but  very  rarely  and  locally,  if  ever,  since 
Palaeozoic  time  began." 

These  highly  crystalline  rocks — gneisses  and  schists  of  various 
kinds — with  occasional  masses  of  marble,  often  suggestive  of  strati- 
fication, constitute  the  earth's  foundation  stones.  In  many  places 
we  can  only  pierce  through  a  comparatively  small  number  of  layers 
in  its  crust,  and  cannot  get  below  either  some  members  of  the 
Secondary  or  Primary  series,  or  a  rock  mass,  comparatively  little 
changed,  but  with  nothing  to  determine  its  precise  age,  as  it  does 
not  contain  fossils.  Such  places  supply  no  information,  since  the 
rocks  have  not  been  sufficiently  crumpled,  and  the  processes  of 
denudation  have  not  cut  deep  enough  into  the  folds  to  show  what 
may  underlie  them.  But  wherever  the  base  of  the  sedimentary 
deposits  has  been  reached,  it  is  found  to  rest  on  a  crystalline  series. 
What  has  been  the  origin  of  the  various  rock  masses  of  which  the 
latter  is  composed  is  a  difficult  question,  upon  which  geologists  at 
present  are  not  agreed.  Probably  some  gneisses  and  schists,  par- 
ticularly the  banded  varieties  of  the  former,  are  in  reality  igneous 
rocks,  which  have  consolidated  under  exceptional  circumstances, 
and  owe  their  structure,  as  already  stated,  to  movements  prior  to 
complete  cooling.  Others,  again,  may  have  also  been  igneous 
rocks,  which,  after  solidification,  were  exposed  to  great  pressures, 
and  so  far  crushed  as  to  assume  a  rude  cleavage,  which,  in  conse- 
quence of  subsequent  mineral  changes,  was  converted  into  a  foliated 
structure.  A  third  group  almost  certainly  consists  of  sediments,  in 
which  still  greater  mineral  changes  have  occurred  ;  for  it  is  difficult 
to  understand  how  marbles,  which  pass  gradually  into  a  mica-schist, 
or  a  quartz-schist,  just  as  a  limestone,  among  ordinary  stratified 
rocks,  can  be  seen  to  pass  into  either  a  shale  or  a  sandstone,  can  be 
attributed  to  any  but  a  sedimentary  origin.  We  cannot,  indeed, 
bring  forward  a  crystalline  limestone  as  a  proof  that  when  it  was 
first  deposited  life  existed  on  the  earth  (on  the  ground  that  ordinary 


THE  ARCH^AN  ERA.  343 

limestones  are  largely  composed  of  calcareous  organisms),  because 
limestones  sometimes  are  formed  by  precipitation,  as  in  the  case  of 
tufas ;  but  since  we  do  not  know  of  any  third  mode  in  which  a  lime- 
stone can  be  produced  at  the  present  time,  we  are  justified  in 
attributing  the  rock  to  one  of  these  two  origins. 

Before  we  proceed  further,  the  less  altered  members  of  the 
Archaean  series  should  be  briefly  noticed.  These,  as  already  inti- 
mated, exhibit  a  great  variety  of  types.  They  consist  of  slates  or 
indurated  shales,  quartzites,  and  conglomerates,  and  occasionally 
sub-crystalline  limestones,  together  with  tuffs,  agglomerates,  and 
contemporaneous  lavas.*  As  a  rule,  a  certain  amount  of  mineral 
change,  an  incipient  metamorphism,  is  exhibited  by  all,  but  the 
alteration  is  not  great ;  the  newer  minerals  are  comparatively  small 
in  size  ;  the  original  character  of  the  rocks  in  every  case  is  readily 
recognized.  They  differ  little,  if  at  all,  from  some  of  the  lower 
members  of  the  Palaeozoic  series,  from  which  probably  they  are  not 
separated  by  any  enormous  interval  of  time.  Of  this  type  the  true 
Huronians  f  of  North  America,  and  similar  rocks  in  other  parts  of 
the  world,  are  representatives. 

The  British  districts  in  which  rocks  occur  belonging  either  cer- 
tainly or  with  very  great  probability  to  the  Archaean  series  may 
be  now  enumerated.  First  come  the  crystalline  rocks  of  the  north- 
western Highlands;  these,  as  already  stated,  certainly  belong  to 
the  Archaean  era,  to  the  end  of  which  the  Torridon  Sandstone  has 
been  lately  assigned.  It  is  no  longer  needful  to  express  any  doubt 
that  a  large  part  of  the  crystalline  masses  in  the  central  Highlands 
are  rightly  regarded  as  Archaean,  and  it  is  quite  possible  that  some 
of  the  fragmental  rocks  which  rest  upon  or  are  infolded  among 
these  may  be  ultimately  proved,  like  the  Torridon  Sandstone,  to  be 
earlier  than  the  Cambrian  system. 

This  crystalline  massif  of  the  Scotch  Highlands  may  be  traced 
through  the  Inner  and  Outer  Hebrides  over  to  the  northwest  of 
Ireland  ;  and  the  wild  mountainous  region  which  extends  roughly 
from  Lough  Foyle  to  Galway  Bay  consists  very  largely  of  ancient 
Archaean  rocks.  In  fact,  the  more  thorough  methods  of  research 
which  have  been  employed  in  the  investigation  of  questions  of  this 

*  Intrusive  igneous  rocks  are  also  present,  but  of  these,  as  they  cannot  be  dated,  no 
account  is  taken. 

f  The  term  has  been  made  to  cover  some  highly  crystalline  rocks  much  more  closely 
allied,  to  the  Laurentian  ;  but  the  rocks  in  Sir  W.  Logan's  typical  sections  were  such  as 
are  described  above. 


344  THE   STORY  OF  OUR  PLANET. 

kind  during  the  last  twenty  years  have  expunged  from  the  maps  of 
Scotland  and  Ireland  the  very  large  areas  of  "  Metamorphosed 
Lower  Silurian "  by  which  they  were  adorned  or  disfigured. 
Archaean  rocks  also  occur  in  Anglesey  and  Carnarvonshire.  In 
the  former  various  crystalline  schists  are  common,  which,  however, 
have  been  much  affected  by  subsequent  pressure,  so  that  the  region 
offers  many  difficulties ;  in  the  latter  the  rocks  are  largely  volcanic 
— lavas  (felstones),  tuffs,  etc.  Near  St.  David's,  in  South  Wales, 
granitic  rocks,  some  felstones,  volcanic  tuffs,  and  diverse  sedimen- 
tary rocks  underlie  a  conglomerate  which  forms  a  convenient  base  to 
the  Cambrian  system  in  that  district.  It  has  been  proposed,  indeed, 
to  include  these  rocks  in  that  system,  both  in  Carnarvonshire  and 
Pembrokeshire ;  but  as  in  each  case  it  has  a  fairly  well-defined  base, 
and  there  is  proof  from  other  districts  that  an  epoch  of  volcanic 
activity  preceded  the  Cambrian,  which  seems  to  have  been  generally 
throughout  Britain  a  period  of  quiet  subsidence  and  deposition  of 
sediment,  this  group  of  rocks,  which  is  one  of  considerable  thick- 
ness and  importance,  appears  to  be  more  naturally  grouped  with 
the  Archaean.  At  Hartshill,  in  Warwickshire,  at  the  Lickey  Hills, 
between  Birmingham  and  Bromsgrove,  and  in  the  Wrekin  and  its 
neighborhood,  a  volcanic  series  underlies  a  quartzite  which  has  now 
been  recognized  as  "  basement  Cambrian."  Hence  the  volcanic 
rocks  belong  to  a  late  part  of  the  Archaean  era.  Formerly  the  hard 
argillaceous  and  arenaceous  rocks  of  the  Longmynd  Hills  were 
regarded  as  Cambrian,  but  they  have  been  shown  by  recent  re- 
searches to  lie  beneath  the  base  of  that  system.  At  Charnwood 
Forest,  in  Leicestershire,  slates,  with  a  few  bands  of  quartzite, 
volcanic  agglomerates,  tuffs,  and  lavas,  crop  up  like  an  island  in  the 
Trias.  The  age  of  these  rocks  is  uncertain,  but  unquestionably 
they  are  very  old  and  bear  a  general  resemblance  to  admittedly 
Archaean  rocks  in  other  districts,  so  that  this  era  is  more  probable 
than  any  other.  A  rock  similar  to  one  of  the  Charnwood  group 
has  been  struck,  715  feet  from  the  surface,  in  a  boring  at  Orton,  in 
Northamptonshire,  twenty-five  miles  away  to  the  southeast,  and 
late  Archaean  rocks  might  probably  be  pierced  at  comparatively 
moderate  depths  in  many  parts  of  central  England. 

The  Malvern  Hills— "  for  mountains  counted  not  unduly  " — are 
carved  out  of  a  mass  of  very  ancient  crystalline  rocks  which  are 
undoubtedly  Archaean,*  and  similar  rocks  are  exposed,  though 

*  The  "  Hollybush  sandstone,"  by  which  they  are  overlain  at  the  southwestern  end,  is 
now  identified  as  basement  Cambrian. 


THE  ARCH&AN  ERA.  345 

rather  imperfectly,  at  the  southern  end  of  the  Wrekin  massif. 
The  rugged  region  about  Start  Point,  Prawle  Point,  and  Bolt  Head, 
in  South  Devon,  consists  of  schists — chloritic  and  micaceous — 
which  are  clearly  disconnected  from  the  Palaeozoic  slates  and  cleaved 
grits  to  the  north,  and  thus  are  probably  Archaean.  The  cliffs  also 
all  round  the  Lizard  district,  in  Cornwall,  consist  of  crystalline 
rocks.  The  date  of  these  cannot  be  fixed,  but  good  reason  can 
be  shown  for  regarding  as  Archaean  at  least  the  earlier  members 
of  the  group,  or  those  which  have  a  bedded  aspect.  Very  similar 


FIG.  127. — POLISHED  SLAB  OF  EOZOON  CANADENSE. 

(Natural  Size.)     The  dark  part  is  Serpentine  ;  the  white  Calcite. 

rocks  occur  in  Sark,  and  most  of  the  crystalline  rocks  in  the  Channel 
Islands  can  be  proved  to  be  older  than  the  earliest  members  of  the 
Cambrian  system. 

On  the  continent  of  Europe  Archaean  rocks  can  be  identified 
with  more  or  less  certainty  in  Brittany,  Normandy,  Auvergne,  and 
in  the  Alps,  from  one  end  of  the  chain,  to  the  other,  in  parts  of 
Spain,  Portugal,  Austria,  Bohemia,  Germany,  and  of  Eastern  Hun- 
gary and  Turkey ;  they  form  almost  the  whole  of  the  Scandinavian 
peninsula,  and  the  district  west  of  a  line  joining  St.  Petersburg  with 
Archangel.  The  Archaean  rocks  of  North  America  have  been 
already  mentioned,  and  the  era  is  doubtless  represented  in  the  other 
quarters  of  the  world,  but  in  regard  to  these  our  knowledge  at 
present  is  so  imperfect  that  a  bare  mention  of  the  fact  must  suffice. 

The  traces  of  life  which,  as  already  intimated,  have  been  found 
in  the  Archaean  rocks  next  claim  a  brief  notice.  The  few  which 
are  indisputable  have  been  detected  only  in  the  latest  members  of 
the  series,  in  rocks  which  till  quite  recently  were  generally  regarded 
as  Cambrian,  and  are  probably  not  separated  from  that  system  by 


346 


THE   STORY  OF  OUR  PLANET. 


any  very  great  interval.  From  the  rocks  of  the  Longmynds  come 
rather  ill-preserved  markings  which  have  been  referred  with  proba- 
bility to  the  shield  of  a  trilobite.  At  Bray  Head,  Wicklow,  a 
curious  structure  has  been  found,  something  like  the  impression  of 
a  small  branching  seaweed.*  From  Howth  come  ill-preserved,  tiny 
spherical  bodies,  which  may  be  radiolaria.  At  all  these  places  the 
tracks  and  burrows  of  worms  may  be  seen. 

When  these  comparatively  unaltered  rocks  are  quitted  for  the 
more  crystalline  and  older  members  of  the  series,  an  impenetrable 
cloud  settles  down  upon  the  beginning  of  the  history  of  life.  The 


FIG.  128. — STRUCTURE  OF  EOZOON  CANADENSE  :  FROM  A  THIN  SECTION. 

Magnified  about  too  Diameters  (after  Carpenter), 

schists  of  stratified  origin  may  have  contained  fossils,  but  they  have 
undergone  such  marked  mineral  changes  as  to  obliterate  all  traces 
of  organic  structures.  Some  authors,  indeed,  have  referred  to  the 
frequent  presence  of  limestone  and  the  occasional  occurrence  of 
graphite  as  proofs  that  living  creatures  existed  even  in  these 
remote  ages ;  but  a  limestone,  as  has  been  already  said,  may 
be  formed  by  precipitation — like  salt  or  gypsum — and  there  is  no 
reason  why,  under  suitable  circumstances,  graphite  may  not  result 
from  the  dissociation  of  carbonic  acid  or  of  carbonates.  Hence  it 


*  The  genus  is  named  0/J/iamia,  and  there  are  at  least  two  distinct  forms.  Some  con- 
sider it  to  be  an  alga,  some  a  hydrozoOn,  some  a  polyzoon.  It  is  most  probably  organic, 
and  that  is  about  all  which  can  be  said  at  present.  It  has  been  found  elsewhere — e.  g. , 
in  the  Ardennes  and  in  Spain. 


THE  ARCH&AN  ERA. 


347 


is    unsafe   to  say  more  than  that  the  occurrence  of   these  rocks 
indicates  the  possibility  that  life  had  already  begun. 

There  is,  however,  one  very  remarkable  structure  which  many 
competent  judges  consider  to  be  an  indubitable  relic  of  an  organism. 
Attention  was  drawn  to  this  about  thirty  years  since,  when  it  was 
named  Eozoon,  the  dawn-animal,  with  the  specific  title  Canadense, 
from  the  country  where  it  was  first  discovered.  This  is  a  structure 
which  is  so  singular,  and  has  provoked  so  much  controversy,  that 
it  claims  something  more  than  a  passing  notice  ;  for  if  its  organic 
nature  can  be  established,  life  had  begun  about  the  middle  of  the 
Laurentian  rocks,  and  must  be  carried  very  far  back  in  the  Archaean 
era.  A  specimen  of  Eozoon  consists  of  two  minerals,  both  exhibiting 
a  certain  crystalline  structure,  the  one  calcite  or  dolomite,  the  other 
a  greenish  mineral,  either  serpentine  or  some  magnesian  silicate, 
generally  hydrous.  The  two  are  roughly  interbanded,  and  the  latter 
shows  a  tendency  to  assume  a  nodular  form,  as  if  it  might  occupy  a 
series  of  chambers  of  oval  shape,  opening  one  into  another,  and 
arranged  in  successive  layers.  (See  Fig.  129.)  The  engraving  on 
p.  345  (Fig.  127)  gives  a  fair  idea  of  the  general  appearance  of  a 
polished  section  of  Eozoon.  On  examining  thin  slices  of  the  rock 
under  the  microscope  the  silicate  is  sometimes  seen  to  be  bordered 
with  a  zone,  or  succession  of  zones,  as  exhibited  in  the  drawing 
(Fig.  128)  at  a  a,  consisting  of  calcite,  which  is  pierced  by  number- 
less minute  "  bristles,"  or  threads,  of  the  former  mineral.  Beyond 
this  the  mass  of  the  calcite  (c)  is  occasionally  traversed  by  curious 
branching  canals,  as  they  seem 
(b],  which  are  sometimes  occu- 
pied by  the  same  mineral, 
sometimes  by  serpentine  or 
some  other  mineral.  As  a  rule, 
these  appear  and  disappear 
irregularly,  and  seem  to  be 
least  frequent  where  the  cal- 
cite is  most  obviously  crystal- 
line. The  various  parts  of  a  ""%»  •/!]•  /"-. 

the  Eozoon  are  connected  as       t  --;    -''•/    /"""'"         ' 

in  the  annexed  diagram  (Fig. 

129),  where  ABC  represent 

the    supposed    chambers,  b  b 

the  intervening  calcite,  a  a  the  bordering  zone,  d  the  canal  system, 

and  c  an  occasional  passage,  leading  from  layer  to  layer.     All  this 


FIG.  129. — DIAGRAMMATIC  SECTION  OF 
EOZOON  CANADENSE. 


348 


THE   STORY  OF  OUR  PLANET. 


FIG.  130.— VERTICAL  SECTION  OF  A  NUMMULITE. 

(Magnified.) 


is  very  suggestive  of  an  organic  structure,  and  zoologists  who  were 
familiar  with  the  foraminifera,*  a  class  of  organisms  belonging  to 
the  protozoa,  were  struck  by  the  resemblance.  Commonly  the 
shells  of  these  are  very  small,  but  fossil  specimens  occasionally 

exceed  an  inch  in  diam- 
eter.  Their  plan  of 
growth,  also,  is  usually 
regular,  but  a  tendency 
to  "  run  wild  "  is  occa- 
sionally exhibited.  In 
the  annexed  diagram  is 
a  section  of  a  well- 
known  type,  which, 
from  its  resemblance  to 
a  coin,  is  called  a  num- 
mulite.  The  section  (at 

right  angles  to  the  flatter  surface)  shows  the  successive  layers  of 
chambers,  large  (c)  and  small  (^),  with  the  dividing  walls  (/;),  indi- 
cating by  the  faint  striations  the  minute  "  foramina "  or  tubules 
which  characterize  this  group  of  animals.  In  some  genera,  as  at  b 
in  this  one  (though  it  cannot  be  shown  in  a  drawing  on  so  small  a 
scale),  the  "  nummuline  layers,"  as  they  are  termed,  around  the 
chambers  are  separated  by  calcareous  material,  called  the  supple- 
mental skeleton,  which  is  traversed  by  a  canal  system.  Thus  one 
of  the  higher  foraminifera  exhibits  a  group  of  structures  which 
closely  resemble  those  detected  in  Eozoon,  the  main  difference 
being  that  the  latter  has  a  far  less  regular  habit  of  growth,  and 
attains  a  much  greater  size.  The  advocates  of  the  organic  origin  of 
Eozoon  urged  that  the  occasional  deviations  from  regularity  and 
resemblances  to  an  inorganic  structure  which  it  presented  were  due 
to  the  disturbing  effect  of  mineralization.  They  also  pointed  out 
that,  even  if  it  were  granted  that  these  structures  could  find  indi- 
vidual parallels  among  minerals,  they  were  only  exhibited  in  com- 
bination by  an  organism,  and  that  this  in  itself  formed  a  strong 
argument  for  referring  Eozoon  to  the  animal  kingdom. 

A  question  of  such  difficulty  must,  however,  be  looked  at  from 
every  point  of  view,  so  that  it  now  becomes  necessary  to  give  a 
brief  description  of  the  appearance  which  Eozoon  presents  when  it 
occurs  in  the  field.  The  account  applies  to  Cote  St.  Pierre,  a  little 


*  See  p.   181. 


THE  ARCH  MAN  ERA. 


349 


settlement  some  dozen  miles  north  of  the  River  Ottawa,  one  of  the 
most  noted  localities,  but  probably  the  others  do  not  present  any 
very  marked  differences.  Omitting  some  minor  particulars,  we  find 
there  a  mass  of  crystalline  limestone,  apparently  intercalated  between 
two  thick  groups  of  gneisses.  This  limestone  in  some  parts  is  fairly 
pure,  in  others  it  contains  certain  silicates.  The  Eozoon  occurs  here 
and  there  sporadically  in  masses  of  irregular  form,  varying  from 
two  or  three  inches  to  as  many  feet  in  diameter.  This  is  how  it 
most  commonly  appears :  At  the  center  is  a  lump,  variable  in 
shape,  of  serpentine  or  of  a  pale  green  pyroxene,*  or  of  both, 


FIG.  131. — DIAGRAM  OF  ROCK  AT  COTE  ST.  PIERRE. 

Lumps  of  light-colored  pyroxene,  sometimes  serpentinous  ;  the  top  one  about  2  feet  3  inches  long  ; 
ringed  in  most  parts  with  Eozoonal  structure  up  to  a  thickness  of  about  4  inches.  The  remainder  of 
the  rock  white  marble,  spotted  with  granular  serpentine. 

round  which  lies  the  Eozoon  for  a  thickness  of  two  or  three  inches, 
and  round  it  comes  the  crystalline  calcareous  rock,  which  is  fre- 
quently spotted  with  grains  of  serpentine  or  pyroxene  about  as  big 
as  mustard  seeds  or  hemp  seeds.  If  Eozoon  is  an  organism,  these 
grains  must  also  have  an  organic  origin,  and  be  the  casts  either  of 
smaller  foraminifera  or  of  separate  chambers  of  the  larger  mass. 
This,  however,  though  not  without  a  precedent,  would  imply  that 
the  process  of  infiltration  was  unusually  rapid.  The  presence  of 
the  core  of  serpentine  or  pyroxene  must  be  accounted  for  by  sup- 


*  A   silicate   of  magnesia,  lime,  and  iron.     The  pale  varieties  (with   little  iron)  pass 
readily  into  a  kind  of  serpentine. 


35°  TffE  STOKY  OF  OUR  PLACET. 

posing  that  the  inner  part  of  the  organism  had  perished,  and  the 
space  been  filled  up  with  solid  silicate,  the  true  structure  being 
retained  only  by  the  outer  and  more  perfect  layers.  But  this  does 
not  seem  a  very  probable  hypothesis.  The  rock  also  has  undergone 
very  great  molecular  changes,  in  common  with  the  rest  of  the  series, 
for  in  no  part  of  it  does  the  slightest  trace  of  a  sedimentary  origin 
remain,  and  this  makes  it  very  unlikely  that  a  delicate  organic  struc- 
ture should  have  been  preserved. 

As  a  further  argument  against  the  organic  origin  of  Eozoon,  it  is 
maintained  that  the  chambered  structure  is  less  regular  than  is  usual 
in  an  animal,  as  may  be  seen  by  a  comparison  of  Fig.  127  with  Fig. 
130,*  and  resembles  the  mineral  banding  common  in  many  crystal- 
line rocks — the  result,  probably,  of  some  process  of  segregation.  It 
is  also  affirmed  that  the  nummuline  layer  when  decalcified  cannot 
be  distinguished  from  a  fibrous  structure  commonly  exhibited  by 
certain  serpentines,  and  the  "  canal  system  "  is  compared  with  certain 
minute  branching  forms  assumed  by  some  minerals.  We  find  occa- 
sionally, on  splitting  open  a  piece  of  compact  rock,  that  a  dark 
mineral  (usually  an  oxide  of  manganese)  has  been  deposited  between 
two  surfaces  where  cohesion  has  been  imperfect,  and  has  so  curiously 
imitated  vegetable  forms  that  it  might  be  readily  mistaken  for  a 
(ossil  plant.  Sometimes  also  in  examining  thin  slices  of  rock  under 
die  microscope  we  notice  an  intergrowth  of  two  minerals  (generally 
quartz  and  felspar)  which  very  closely  resembles  the  canal  system. 
So  there  is  evidently  much  to  be  said  on  both  sides  of  the  question. 
At  first  the  balance  of  scientific  opinion  was  in  favor  of  regarding 
Eozoon  as  a  fossil.  It  was  claimed  for  the  animal  kingdom  by  men 
exceptionally  well  acquainted  with  the  structures  of  the  lower 
organisms,  and  the  few  advocates  of  the  other  view  certainly  failed 
in  making  out  a  strong  case.  But  their  cause  of  late  years  has  been 
adopted  by  much  more  competent  advocates,  and  it  must  be 
admitted  that  the  arguments  founded  on  a  microscopic  study  of  the 
structure  seem  now  to  be  very  nearly  balanced,  but  that  the  evidence 
obtained  by  looking  at  Eozoon  in  its  association  with  the  Lauren- 
tian  rock  masses  is  distinctly  favorable  to  the  mineral  origin. f 
Still,  if  this  be  so,  the  structure  is  a  very  peculiar  and  exceptional 


*  It  should  be  mentioned  that  some  of  the  foraminifera  follow  a  less  regular  plan  of 
growth  thaji  the  nummulite. 

f  The  writer  feels  bound  to  state  that  up  to  1884  he  was  a  believer  in  the  organic  nature 
&f  Eozoon,  but  was  beginning  to  feel  the  general  difficulties  presented  by  the  preservation 


THE  ARCHAEAN  ERA.  35  l 

one,  so  that  the  controversy  at  present  can  be  hardly  regarded  as 
closed  ;  certainly  much  has  still  to  be  learned  about  the  genesis  of 
the  structure  itself,  and  the  history  of  the  peculiar  group  of  marbles 
to  which  it  belongs. 

We  have  seen  that  the  earlier  Archaean  rocks  are  invariably  in  a 
crystalline  condition,  and  that,  whenever  it  is  possible  to  arrive  at. 
any  conclusion  in  regard  to  their  origin,  they  prove  to  be  either 
igneous  rocks  of  an  abnormal  character — that  is,  they  probably 
crystallized  under  conditions  now  exceptional,  but  formerly  general 
— or  they  are  sedimentary  strata  which  have  undergone  very  great 
changes.  Metamorphism,  as  has  been  already  stated,  is  brought 
about  by  one  or  more  of  these  agents — water,  pressure,  and  heat — 
but  careful  work  in  the  field  and  with  the  microscope  makes  it  possi- 
ble to  distinguish  which  of  them  has  been  chiefly  operative  in  any 
particular  case.  Accordingly  we  find  that  the  Archaean  schists 
differ  in  structure  from  sediments  which  have  been  modified  mainly 
by  pressure,  and  approach  those  which  have  been  affected  by  a  high 
temperature,  though  they  can  be  readily  distinguished  frorn  ordinary 
cases  of  contact-metamorphism,*  as  this  is  called.  The  inference 
thus  seems  legitimate  that  these  schists  were  exposed  for  a  con- 
siderable time  to  the  action  of  a  rather  high  temperature.  Doubt- 
less water  was  present,  and  the  rock  Was  subject  to  a  considerable 
pressure,  each  of  these  conditions  being  no  doubt  an  essential,  but 
not  the  primary  factors  in  bringing  about  the  result.  These  schists 
must  have  been  raised  to  a  temperature  above  that  which  a  rock 
attains  by  being  depressed  to  a  depth  of  ten  or  fifteen  thousand  feet 
below  the  earth's  surface,  because  there  is  no  difficulty  in  finding, 
for  purposes  of  comparative  study,  Palaeozoic  rocks — if  not  any  of 
later  date — which  have  been  buried  beneath  at  least  that  thickness 
of  sediment,  and  yet  have  returned  to  the  surface  practically  un- 
altered.f  These  great  mineral  changes,  which  have  converted  a 
sediment  into  a  rather  coarsely  crystalline  schist,  appear  to  have 

of  an  organism  in  these  rocks.  In  the  summer  of  that  year  he  had  the  great  pleasure  and 
advantage  of  visiting  Cote  St.  Pierre  with  Sir  W.  Dawson,  but  he  did  not  return  with  his 
wavering  faith  confirmed. 

*  Crystalline  rocks,  sometimes  foliated,  are  produced  by  this  action,  but  it  is  convenient 
to  exclude  them,  as  a  rule,  from  the  term  schist. 

f  Assuming  the  conditions  to  be  the  same  as  now,  a  rock  by  being  buried  12,000  feet 
below  the  surface  would  have  its  temperature  raised  by  about  200°  F. — i.  e.,  the  tempera- 
ture of  the  mass  would  be  rather  above  that  at  which  water  boils  on  the  surface.  This 
would  be  favorable  to  mineral  change,  but  it  obviously  has  been  insufficient  to  produce 
any  effects  on  an  important  scale. 


35 2  THE   STORY  OF  OUR  PLANET. 

taken  place  at  a  period  comparatively  early  in  the  rock's  history. 
The  oldest  Palaeozoic  strata  only  exhibit  a  slight  approach  to  them  ; 
rocks  of  later  date  never  give  more  than  a  "  colorable  imitation." 
Though  it  has  been  often  asserted,  it  has  not  yet  been  proved  that 
a  sedimentary  rock  has  been  ever  converted  into  a  true  schist  since 
Archaean  times.  Enough  is  now  known  to  justify  the  assertion  that 
if  such  a  thing  can  be  found,  it  is  very  rare  and  local.  These  state- 
ments, then,  which  are  matters  of  fact  rather  than  of  opinion,  sug- 
gest that  in  Archaean  times  either  the  earth's  crust  as  a  whole  was 
at  a  higher  temperature  than  it  is  now,  or  that,  if  the  surface  was 
nearly  at  the  present  temperature,  there  was  then  a  more  rapid  in- 
crease in  descending  below  it.  The  rate  is  now,  roughly,  i°  F.  for 
60  feet  of  descent.  On  the  assumption  that  the  earth  was  once  in 
an  incandescent  condition,  and  has  cooled  by  radiation,  Lord  Kelvin 
has  shown  that  though  the  heat  of  the  interior,  after  a  compara- 
tively short  time,  would  cease  to  produce  any  sensible  effect  upon 
the  surface,  the  temperature,  at  the  end  of  one  twenty-fifth  of  the 
whole  time  which  has  elapsed  between  the  first  crusting  over  of  the 
globe  and  the  present  age,  would  rise  i°  F.  for  every  10  feet  of 
descent.  The  loss  of  heat  from  the  outer  part  of'  the  crust  at  first 
was  comparatively  rapid,  but  it  became  continually  slower.  For 
some  while  after  the  epoch  just  named,  foot  after  foot  would  be 
rather  rapidly  added  to  the  interval  corresponding  with  each  rise  of 
a  degree  in  temperature,  until,  probably,  before  the  world  had 
advanced  very  far  in  the  Primary  era  the  conditions  had  approached 
so  near  to  those  now  existing  that  the  depression  of  a  mass  of  rock 
to  a  couple  of  miles  below  the  surface  brought  it  into  a  zone  of 
temperature  only  slightly  higher  than  would  be  found  at  the  present 
time. 

Accordingly  since  there  must  have  been  an  epoch,  whether  any 
record  now  remains  of  it  or  not,  when  a  temperature  equal  to  the 
melting  point  of  iron  would  be  reached  within  four  miles  from  the 
surface,  and  everything  at  a  depth  of  10,000  feet  would  be  at  a  dull 
red  heat ;  since  there  is  no  evidence  that  any  such  conditions  con- 
tinued even  into  Palaeozoic  times,  during  which,  so  far  as  we  can 
tell,  the  temperature,  in  the  earliest  epochs,  did  not  increase  at  a 
rate  very  appreciably  more  rapid  than  now:  since  the  evidence,  so 
far  as  it  goes,  indicates  a  quicker  increase  in  the  earliest  times,  and 
the  oldest  rocks  are  always  those  which  have  been  very  greatly 
affected  presumably  by  a  high  temperature — we  are  led,  in  accord- 
ance with  the  usual  principles  of  induction,  to  infer  that  the 


THE  ARCH&AN  ERA.  353 

Archasan  schists  are  records  of  the  earliest  chapters  in  the  earth's 
history.  It  is  also  probable  that  some  of  the  gneisses  and  abnormal 
igneous  rocks  which  are  so  associated  with  them  as  to  suggest  con- 
temporaneity or  priority  of  formation  rather  than  subsequent 
intrusion,  may  be,  if  not  actually  part  of  the  primitive  crust  of 
the  earth,  masses  extruded  at  a  time  when  molten  rock  could  be 
reached  everywhere  near  to  the  surface,  and  when  the  process  of 
cooling,  even  at  a  very  moderate  depth,  was  much  slower  than  it 
became  in  the  ages  after  the  earth  had  begun  to  be  occupied  by 
living  creatures. 


CHAPTER  IV. 

THE   BUILDING   OF   THE   BRITISH   ISLES. 

THE  geography  of  the  globe  at  the  present  epoch  is  the  outcome 
of  its  geography  in  past  ages.  Each  mass  of  land  is  the  result  of 
two  processes — the  one  of  deposition,  the  other  of  sculpturing. 
By  the  former  its  materials  were  collected  and  built  up,  by  the 
latter  its  surface  was  molded  and  its  boundaries  were  defined. 
These  chapters  in  the  physical  history  of  each  region  may  be 
recovered.  This  is  the  task  of  the  geologist :  to  delineate  in  a 
series  of  sketches  the  changing  scenes — as  sea  was  replaced  by 
land,  or  land  by  sea ;  as  island  groups  coalesced  into  continents,  or 
continents  were  severed  and  submerged ;  as  mountain  chains  arose, 
and  as  even  they,  at  last,  were  brought  low.  The  materials  which 
enter  into  the  composition  of  a  deposit,  the  changes  which  the 
latter  exhibits  as  it  is  traced  across  the  country,  afford  clews  to  the 
nature,  the  position,  and  the  grouping  of  the  old  land  masses,  so 
that  the  microscope  in  the  hands  of  workers  who  are  capable  of 
looking  from  the  small  to  the  great  is  a  bridge  across  vast  intervals 
of  time,  like  the  spectroscope  or  the  telescope  across  the  abysses  of 
space.  The  difficulty  of  any  attempt  to  reconstruct  the  physical 
geography  of  past  ages  necessarily  increases  with  the  distance  of 
the  time,  for  the  evidence  must  obviously  become  more  and  more 
imperfect  and  fragmentary.  The  older  a  mass  of  rock  is  the  more 
unfrequent  and  limited  are  likely  to  be  its  outcrops ;  or,  in  the 
rare  cases  where  land  has  remained  above  the  sea  for  long  epochs, 
the  more  carious,  worn,  and  ruinous,  and  so  the  less  suited  for 
examination,  will  its  surface  have  become.  From  this  it  follows 
that  any  attempt  to  reconstruct  the  physical  geography  of  a  district 
in  the  earlier  part  of  the  Primary  era  is  almost  hopeless  ;  to  succeed 
in  indicating  the  position  of  land  and  sea  is  the  utmost  that  can  be 
expected  ;  but  as  time  proceeds,  the  difficulties  gradually  diminish. 
Want  of  space  precludes  any  attempt  to  enter  into  a  detailed  history 
of  each  region  on  the  surface  of  the  earth,  and  in  not  a  few  the  task 
would  be  hopeless  at  present  for  want  of  sufficient  materials ;  but 
we  will  endeavor  to  give  some  idea — though  even  this  must  be  in 


THE   BUILDING   OF    THE  BRITISH  ISLES.  355 

bare  outline — of  the  building  of  the  British  Isles  during  the  several 
geological  periods,  and  then  indicate,  still  more  imperfectly,  the 
probable  story,  or  rather  some  fragments  of  the  story,  for  each  con- 
tinent. These  isles,  as  already  intimated  (pp.  52  and  57),  are  in 
close  connection  with  the  northwest  part  of  the  continent  of  Europe 
(Fig.  19,  p.  53)  ;  their  geology  is  a  sample — we  might  almost  say 
an  epitome — of  its  geology  ;  their  history  is  really  inseparable  from 
its  history ;  so  that  in  the  endeavor  to  decipher  the  story  from  our 
own  country  we  shall  be  led,  almost  insensibly,  to  recover  it  for  a 
considerable  area  of  the  adjoining  mainland. 

It  is  a  hopeless  task  to  attempt  to  reconstruct  the  physical 
geography  of  Britain  prior  to  the  beginning  of  the  Cambrian 
period.  Even  for  this  time  the  materials  are  very  fragmentary. 
Only  in  the  northern  part  of  Scotland  and  the  northwest  of  Ireland 
are  any  large  masses  of  the  earlier  Archaean  rocks  still  visible. 
These,  at  any  rate  in  the  former,  appear  to  have  undergone  great 
denudation  in  the  epoch  immediately  preceding  the  Cambrian ; 
their  ruins  formed  the  Torridon  Sandstone,  and  the  process  of 
destruction  obviously  continued  during  the  earlier  part  of  the 
Cambrian  period.  In  some  districts  of  Britain — as,  for  instance,  in 
northwest  and  southwest  Wales,  in  Shropshire,  Warwickshire,  and 
probably  Leicestershire — the  Archaean  era  was  closed  by  oscillatory 
movements  of  the  earth's  crust  and  sporadic  volcanic  activity. 
These  disturbances,  as  is  frequently  the  case,  appear  to  have  been 
the  prelude  to  a  long-continued  subsidence  of  the  crust,  affecting  a 
considerable  portion  of  Britain,  during  which  the  Cambrian  strata 
were  deposited.- 

These,  in  Britain,  are  divided  into  four  sub-groups — the  Harlech 
or  Lower  Cambrian  beds,  which  may  have  a  maximum  thickness  of 
some  8000  feet ;  the  Menevian,  a  comparatively  thin  but  palaeonto- 
logically  well-marked  group,  measuring  only  about  700  feet;  the 
Lingula  Flags,  sometimes  as  much  as  5000  feet ;  and  the  Tremadoc 
Slates,  about  1000  feet.  In  Scotland  the  scarcity  of  fossils  makes 
it  difficult  to  know  to  what  extent  deposits  of  Cambrian  age  are 
represented,  and  it  has  only  been  ascertained  quite  recently  by  the 
discovery  of  an  Olenellus*  that  the  white  quartzite  of  the  northwest 
Highlands  lies  in  reality  at  the  base  of  the  Cambrian  system.  Its 
materials  evidently,  like  those  of  the  preceding  Torridon  Sandstone, 
were  derived  from  the  coarse  crystalline  rocks  of  the  adjacent 
region  ;  so  that  the  existence  of  a  considerable  mass  of  land  formed 

*  A  trilobite,  one  of  the  earliest  known  genera. 


356 


THE   STORY  OF   OUR  PLANET. 


of  such  rocks  is  indicated,  which  lay,  probably,  to  the  northwest. 
In  like  manner  the  Lower  Cambrian  or  Harlech  beds  in  England 
generally  intimate  by  their  materials  the  proximity  and  the  destruc. 
tion  of  a  land  composed  of  crystalline  rocks. 
It  is  very  doubtful  whether  any  part  of  the 
Cambrian  system  can  be  identified  in  Ire- 
land. In  County  Wicklow  rocks  exist  which 
originally  must  have  been  sandstones  and 
muds  ;  these  were  formerly  referred  to  the 
Harlech  group,  but  they  are  now  considered 
to  be  slightly  earlier.  The  occurrence  in 
Connemara  of  Ordovician  rocks,  containing 
numerous  fragments  of  the  Archaean  crystal- 
line masses,  indicates  the  gradual  subsi- 
dence of  a  land  region  which  probably 
extended,  at  any  rate  in  earlier  Cambrian 
times,  over  a  large  area  both  west  and  east 
of  that  country.  An  overlapping  of  the 
Cambrain  deposits  in  the  Harlech  and  the 
Carnarvonshire  areas  is  exhibited  in  North 
Wales,  for  in  Anglesey,  according  to  our 
present  knowledge,  Upper  Cambrian  or 

Ordovician  strata  rest  on  various  pre -Cambrian  recks.  Hence  the 
sea  must  have  gradually  deepened  and  crept  northward  over 
Anglesey,  which,  for  a  time,  formed  part  of  the  coast  line.  Indica- 
tions of  another  coast  line  may  be  detected  in  Cornwall,  and  picked 
up  again  in  the  Channel  Islands,  Brittany,  and  Normandy.  Alto- 
gether it  seems  probable  that  the  site  of  England  and  Wales,  perhaps 
also  of  Scotland,  in  Cambrian  times,  was  a  rather  shallow  sea,  the 
area  of  which  gradually  extended  as  its  bed  sank,  and  in  which 
sediment  was  plentifully  deposited,  supplied  from  a  large  mass  of 
land  (in  which  Ireland  may  have  been  included),  at  no  great  distance 
to  the  northwest,  west,  and  southwest. 

The  Ordovician  system  is  subdivided  into  the  following  groups : 
The  Arenig,  attaining  a  maximum  thickness  of  2500  feet ;  the 
Llandeilo,  amounting  to  about  3000  feet ;  the  Caradoc  or  Bala 
group,  very  variable  in  thickness,  but  sometimes  exceeding  4000 
feet ;  and  the  Lower  Llandovery,  a  comparatively  unimportant 
group,  evidently  transitional  in  character,  which  varies  from  about 
600  to  1 200  feet.  Ordovician  rocks  occupy  a  considerable  part  of 
Wales,  more  especially  on  the  western  side  ;  they  occur  on  the  eastern 


FIG.  132. — A  LOWER 
CAMBRIAN  TRILO- 
BITE  (Paradoxides). 


THE   BUILDING  OF    THE  BRITISH  ISLES.  357 

border  and  in  Shropshire  ;  also  in  the  Lake  District,  in  western  York- 
shire, and  in  the  Isle  of  Man.  They  are  occasionally  exposed  in  the 
southern  uplands  of  Scotland,  as  about  Girvan  and  Moffat  ;  they  crop 
out  in  the  northwest  and  northeast  of  Ireland,  and  have  been 
detected  in  Cornwall,  in  the  vicinity  of  Veryan  Bay,  and  in  the  Mene- 
age  district.  Probably  a  large  part  of  Great  Britain  and  Ireland  was 
covered  by  sea  during  this  period,  though  the  expanse  of  water  may 
have  been  interrupted  locally  by  islands.  In  Arenig  times  volcanoes 
were  active  in  North  Wales.  Relics  of  these  are  preserved  in  the 
mountainous  region  which  culminates  in  the  Arenigs,  the  Arans,  and 
Cader  Idris,  as  well  as  in  that  of  the  Berwyn  Hills.  In  Llandeilo 
times  the  seat  of  disturbance  seems  to  have  shifted  southward  to 
Pembrokeshire,  and  northward  to  the  lake  district,  where  ashy 
slates,  tuffs,  volcanic  breccias,  and  lava  streams  make  up  a  mass  of 
rock  not  less  than  10,000  feet  in  thickness,  in  which  not  a  single 
fossil  has  been  discovered.  It  has  been  recently  ascertained  that 
there  was  also  a  considerable  amount  of  volcanic  action  at  this 
epoch  in  the  southern  uplands  of  Scotland.  The  eruptions  of  the 
Lake  District  ceased  early  in  the  Bala  epoch,  but  then  volcanoes 
broke  out  afresh  in  North  Wales — this  time,  however,  in  the  Snow- 
donian  district  and  east  of  it  at  least  as  far  as  the  valley  of  the  Con- 
way.  These  last,  at  any  rate,  must  have  been  submarine,  for  on 
the  peak  of  Snowdon  an  ashy  slate  full  of  characteristic  Bala  fossils 
is  intercalated  between  lava  streams,  the  lower  group  of  which 
forms  the  grand  cliffs  which  overhang  Glaslyn.  The  volcanic  dis- 
turbances, at  the  one  or  the  other  of  these  epochs,  also  affected 
other  areas  in  the  northern  half  of  Wales,  as  far  west  as  the  Lleyn 
and  east  as  the  Corndon  district,  but  in  some  of  them  it  is  more 
difficult  to  ascertain  the  precise  date.  The  geography  of  Great 
Britain  and  Ireland  during  the  Ordovician  period  may  be  concisely 
described  as — a  sea  of  variable  deptlr,  with  a  mass  of  land,  still  large, 
on  the  northwest,  west,  and  southwest.  The  shallower  parts  or  the 
islands  of  this  sea  from  time  to  time  were  disturbed  by  volcanic 
outbursts,  sometimes  of  great  violence.  The  period  was  closed  by 
important  movements  of  the  earth's  crust.  Now  began,  in  all  prob- 
ability, the  mountain  making  of  the  Scotch  Highlands,  affecting  a 
large  district,  of  which  the  northwest  of  Ireland  is  only  a  fragment. 
The  northern  part,  at  least,  of  Wales  was  similarly  disturbed,  and 
by  these  movements  were  produced  the  cleavage  of  its  older 
deposits,  as  well  as  the  interruption  between  them  and  the  base  of 
the  rocks  which  come  next  in  succession. 


35^  THE   STORY  OF  OUR   PLANET. 

The  Silurian  system  is  divided  into  three  groups :  The  Upper 
Llandovery,  which  may  attain  a  thickness  of  looo  feet ;  the  Wen- 
lock,  which  is  often  full  1 500  feet ;  and  the  Ludlow  group,  which 
occasionally  reaches  about  1800  feet.  Deposits  of  Silurian  age 
probably  exist  in  all  parts  of  Wales  not  previously  mentioned,  for 
they  form  a  large  part  of  the  surface  around  the  patches  of  older 
rock ;  they  crop  up,  here  and  there,  through  a  newer  deposit  (the 
Old  Red  Sandstone)  in  the  south,  and  rise  from  beneath  it  on  the 
east.  Similar  evidence  justifies  the  assertion  that  they  extended 
into  the  English  Midlands,  for  an  occasional  outcrop  from  beneath 
newer  rocks  indicates,  like  a  skerry  projecting  from  the  sea,  that  a 
mass  of  rock  is  hidden  beneath  the  surface.  Whether  they  ever 
extended  as  far  as  Leicestershire,  eastern  Warwickshire,  and  North- 
amptonshire is  more  doubtful,  but  they  have  been  struck  in  a  boring 
beneath  Ware,  in  Hertfordshire,  so  that  the  apparent  interruption 
to  the  continuity  of  the  deposit  may  have  been  caused  by  an  island 
which  at  that  time  occupied  the  site  of  the  Midland  counties. 
Certainly  the  sea  extended  northward  over  Cumberland  and  West- 
moreland into  Scotland,  the  greater  part  of  the  southern  uplands 
consisting  of  Silurian  rocks,*  but  very  probably  the  Highlands  had 
now  risen  well  above  water,  and  the  mountain  making  went  on  con- 
tinuously. Silurian  rocks  have  been  found  in  western  Ireland — 
in  Galway,  Mayo,  and  Kerry — and  in  certain  localities  in  the  north- 
east. From  the  former  it  is  evident  that,  as  in  Scotland,  great  earth 
movements  had  preceded  the  deposit  of  the  basement  bed  of  the 
Silurian,f  while  from  the  relation  of  the  older  rocks  of  Dublin, 
Wicklow,  and  Wexford  to  those  which  rest  upon  them  (Old  Red 
Sandstone),  it  seems  more  probable  that  this  region  was  above 
water  in  Silurian  times,  perhaps  forming  part  of  an  island  which 
may  have  extended  to  the  western  margin  of  North  Wales. 

The  Silurian  deposits  furnish  some  interesting  facts  which  have  a 
direct  bearing  on  the  physical  geography  of  the  period.  In  Shrop- 
shire, Herefordshire,  and  Monmouth,  and  to  the  east,  so  far  as 
known,  they  are  very  dissimilar  in  composition  from  their  representa- 
tives in  central  and  northern  Wales,  in  the  north  of  England,  and 
in  southern  Scotland.  The  difference  mainly  is  this :  The  former, 
at  any  rate  after  the  Upper  Llandovery,  include  limestones,  one  of 

*  Here,  as  in  the  Lake  District  and  in  West  Central  Wales,  the  break  between  Ordo- 
vician  and  Silurian  is  slight  or  imperceptible. 

f  Sir  A.  Geikie  has  given  reasons  (Nature,  xl.  p.  323)  to  prove  this,  and  to  make  it 
probable  that  the  disturbances  continued  in  Silurian  times, 


TtiE  BUILDING  OF   THE  BRlflSti  ISLES.  &<) 

which,  the  Wenlock  limestone,  is  fairly  thick  and  extensive,  and  are 
generally  fine-grained,  mudstones  predominating ;  the  others  have 
no  limestones,  but  consist  of  fragmental  materials,  varying  from 
shales  to  fairly  coarse  sandstone.  A  study  of  the  microscopic 
structure  of  the  last  named  proves  that  masses  of  coarse  crystalline 
rock  and  volcanic  materials  must  have  been  undergoing  denudation, 
thus  indicating  the  continued  existence  of  the  northwestern  land 
already  mentioned,  of  which  the  present  Scotch  Highlands  must 
have  formed  a  part,  and  suggesting  that  of  a  region  of  some  size 
and  elevation  to  the  west  of  North  Wales.  The  Silurian  period 
seems  to  have  been,  like  the  Cambrian,  one  of  quiet  and  slow  sub- 
sidence, unruffled  by  volcanic  explosions,  except  in  the  extreme 
west  of  Ireland,  near  Lough  Mask,  and  in  the  wild  headlands  of 
Kerry  about  Dingle  Bay. 

The  Devonian  system  has  not  been  so  generally  divided  into 
groups,  other  than  is  expressed  by  the  use  of  the  terms  Upper, 
Middle,  and  Lower,  as  the  preceding  systems,  but  it  presents  us 
with  two  distinct  types,  being  the  first  instance  in  the  country  of  an 
anomaly  which  afterward  occurs  more  than  once.  The  system  is 
represented  in  one  region  by  strata  of  a  normal  character,  evidently 
deposited  in  the  sea  ;  in  another  by  rocks  which,  whatever  may 
have  been  their  origin,  are  clearly  abnormal.  To  the  former  the 
name  Devonian  properly  belongs  ;  to  the  latter  the  descriptive  title 
of  Old  Red  Sandstone  was  given  at  an  early  date,  and  might  still 
be  retained  to  designate  the  abnormal  type.  In  this  country  the 
relations  of  the  marine  beds  to  deposits  of  earlier  date  are  not  very 
clear.  They  only  crop  out  to  the  south  of  the  Bristol  Channel,  and 
underneath  them  no  Silurian  strata  have  as  yet  been  recognized  ; 
these  are  either  wanting  or  represented  by  unfossiliferous  deposits. 
That  the  Devonian  strata  underlie  the  Carboniferous  system  is  clear, 
for  that  occupies  a  trough,  bounded  on  the  north  and  south  by 
Devonian  rocks.  The  only  difficulty  consists  in  settling  exactly 
where  the  line  between  them  is  to  be  drawn.  But  the  position  of 
the  Old  Red  Sandstone  is  clearly  defined.  There  is  a  gradual  pas- 
sage into  it  from  the  Silurian  system.  There  is  one  no  less  gradual 
from  it  into  the  Carboniferous.  As  the  fossils  characteristic  of  the 
older  deposit  disappear,  the  rocks  assume  a  red  color,  and  become 
sandy.  Their  fossils,  which  usually  are  not  common,  are  of  rather 
peculiar  types.  This  state  of  things  continues  often  for  some 
thousands  of  feet,  then  the  color  begins  to  change,  the  red  sand- 
stones or  marls  are  replaced  by  yellow  or  grayish  calcareous  rocks 


360  THE  STORY  OF  OUR  PLANET. 

or  by  dark  shales,  and  the  fossils  characteristic  of  the  Carboniferous 
system  make  their  appearance. 

For  a  more  complete  knowledge  of  the  marine  deposits  of  the 
Devonian  period  we  must  turn  to  other  countries.  From  these  we 
learn  that  it  is  not  only  entitled  to  the  full  rank  of  a  system,  but 
also  that  it  is  intermediate  between  the  Silurian  and  the  Carbonif- 
erous. The  boundaries  of  the  sea  in  which  it  was  deposited  can  be 
more  easily  discussed  after  the  Old  Red  Sandstone  type  has  been 
described.  The  latter  is  found  in  insulated  patches,  which,  however, 
are  sometimes  very  extensive.  One  covers  a  large  part  of  southern 
and  southeastern  Wales — probably  it  extended  over  all  the  rudely 
triangular  area  between  the  Bristol  Channel,  a  line  drawn  roughly 
from  St.  Bride's  Bay  to  the  Wrekin,  and  one  running  southward 
from  the  latter  to  somewhere  near  the  eastern  end  of  the  Mendip 
Hills.  A  second  occupies  part  of  Northumberland,  and  curves 
round  the  southeast  end  of  the  southern  uplands  of  Scotland.  A 
third  patch  flanks  both  the  northern  side  of  these  hills  and  the 
southern  side  of  the  Highlands,  and  probably  underlies  the  whole  of 
the  central  valley  of  Scotland,  extending  into  northeast  Ireland  ;  a 
fourth  is  situated  on  each  side  of  the  Moray  Firth,  extending  even 
as  far  as  the  Orkney  Islands,  and  running  up  as  well  into  the  Great 
Glen.  These  all  cover  considerable  areas,  but  there  are  also  small 
patches  of  similar  character  in  Lorn  and  in  Donegal.  In  the  south 
of  Ireland  rocks  of  an  Old  Red  Sandstone  type  occur  and  are  well 
developed.  These  pass  up,  as  usual,  into  indubitable  members  of 
the  Carboniferous  system,  but  are  found  to  rest,  with  marked 
unconformity,  on  a  thick  series  of  gritty  beds,  which  overlie  true 
Silurian  rocks,  and  resemble  in  general  character  some  of  those  in 
Devon,  though  as  yet  they  have  not  yielded  any  fossils. 

The  marine  or  normal  Devonian  rocks  are  often  fairly  rich  in 
organic  remains  ;  not  so,  as  a  rule,  those  of  Old  Red  Sandstone  type. 
Neither  are  the  fossils  in  the  latter,  when  they  do  occur,  very  helpful 
in  throwing  light  upon  the  history  of  its  origin.  They  are  chiefly 
plants,  fishes,  and  a  peculiar  group  of  crustaceans,  which  will  be 
more  particularly  noticed  in  a  later  chapter.  They  are  not,  indeed, 
altogether  restricted  to  these  deposits,  and  elsewhere  have  occurred 
with  fossils  indubitably  marine,  and  one  or  two  such  fossils  actually 
have  been  found  in  the  Old  Red  Sandstone  of  South  Wales ;  but 
the  evidence  on  the  whole  makes  it  probable  that  the  Old  Red 
Sandstone  was  not  deposited  in  the  sea.  By  most  geologists  it  is 
regarded  as  a  lacustrine  deposit,  and  geographical  names  have  been 


THE  BUILDING  OF   THE  BRITISH  ISLES.  361 

assigned  to  the  several  areas.*  Some,  however,  think  that  the  sea 
may  have  occasionally  gained  access  to  the  lakes  which  covered 
South  Wales  and  the  central  valley  of  Scotland — if,  indeed,  the 
former  were  not  always  an  estuary.  In  that  case  it  would  have 
been  in  direct  continuity  with  the  sea  which  overspread  North 
Devon,  the  deposits  of  which  now  and  again  bear  a  resemblance  to 
those  on  the  north  side  of  the  Channel.  This  sea  also  probably 
covered — at  any  rate  during  the  earlier  part  of  the  time — the 
southwest  of  Ireland. 

Be  this  as  it  may  two  facts  are  certain:  One,  that  during  this 
period  Great  Britain  was  the  scene  of  severe  volcanic  eruptions. 
South  Wales,  indeed,  appears  to  have  been  undisturbed ;  so  also, 
with  some  comparatively  slight  exceptions,  were  Devonshire  and 
the  district  of  the  Moray  Firth.  Not  so,  however,  the  other  regions. 
The  Cheviots,  the  Pentlands,  the  Sidlaws,  the  Ochils,  and  many 
another  northern  group  of  hills,  are  mainly  formed  of  piles  of  lava, 
agglomerate,  and  tuff,  ejected  by  the  Old  Red  Sandstone  volcanoes. 
These  belong  almost  always  to  the  lower  part  of  the  system.  Not 
only  this,  but  the  mountainous  region  also — especially  in  the  cen- 
tral Highlands — is  repeatedly  riven  by  dykes  of  compact  igneous 
rock,  and  not  seldom  invaded  by  huge  masses  of  granite.  Almost 
all  the  former,  and  not  a  few  of  the  latter,  probably  belong  to  this 
era,  and  indicate  that  during  Old  Red  Sandstone  times  a  large  part 
of  Scotland  was  studded  with  active  volcanoes,  many  of  which  prob- 
ably were  on  a  scale  far  grander  than  Vesuvius. 

The  other  fact  is  this — that  during  the  Old  Red  Sandstone  period 
denudation  was  active,  and  affected  a  large  tract  of  land.  The  sand- 
stones indicate  the  destruction  of  huge  masses,  either  of  earlier 
sandstones  or  of  fairly  coarse  granitoid  rocks.  The  pebble  beds 
which  abound  in  Scotland  are  crowded  with  fragments  derived  not 
only  from  the  volcanoes  just  mentioned,  but  also  from  the  Archaean 
and  earlier  Primary  rocks  of  the  Highlands.  The  great  northwestern 
land,  remnants  of  which  are  left  to  us  in  the  latter  district  and  in 
the  northwest  of  Ireland,  must  by  this  time  have  developed  into  a 
mountain  region,  seamed  with  torrents  and  rivers,  which  was  being 
sculptured  into  peaks  and  glens  and  valleys.  A  period  of  earth 
movement,  which  lasted  all  through  the  Silurian,  was  probably 

*  In  Scotland  the  southeastern  area  is  called  Lake  Cheviot  ;  the  central  one,  Lake  Cale- 
donia ;  the  northeastern  one,  Lake  Orcadie  ;  and  the  small  western  basin,  Lake  Lorn. 
Lake  Fanad  is  the  name  proposed  for  the  one  in  Donegal,  and  that  in  Wales  is  simply 
called  the  Welsh  Lake. 


362  THE  STORY  OF  OUR  PLANET. 

ended  by  an  episode  of  more  active  disturbance,  which  produced 
the  southern  uplands — perhaps  also  some  of  the  most  remarkable 
dislocations  of  the  Highlands  themselves — which  correspondingly 
quickened  the  action  of  the  denuding  forces,  and  resulted  in  the 
comparatively  rapid  accumulation  of  great  masses  of  conglomerate 
and  sandstone.  These  may  have  been  formed  in  lakes — certainly 
their  present  distribution  accords  well  with  that  idea — but  in  any 
case  we  need  not  hesitate  to  recognize  in  them  the  debris  of  a 
mountain  region,  and  proofs  of  the  marked  change  which  had  passed 
over  the  eastern  margin  of  that  great  land  area  of  which  indications 
have  been  afforded  from  so  early  an  epoch.  They  tell  us  that  the 
Scotch  Highlands,  in  their  present  form,  are  only  the  ruins  and 
the  remnants  of  a  mountain  chain  which  has  existed  from  the  very 
beginning  of  the  Devonian  period. 

The  Old  Red  Sandstone  itself  indicates  that  even  while  it  was 
being  deposited  disturbances  had  not  ceased.  In  all  the  northern 
regions  one  well-marked  break  may  be  generally  recognized,  and,  as 
some  think,  a  second  also.  An  unconformity — conspicuous  on  both 
sides  of  the  central  valley — separates  the  Upper  Old  Red  Sandstone, 
which  passes  on  into  the  Carboniferous,  from  the  Lower  Old  Red 
Sandstone,  which  no  less  clearly  passes  down  into  the  Silurian. 
True,  there  is  little  sign  of  this  unconformity  in  the  Moray  Firth  dis- 
trict or  in  South  Wales,  but  it  is  well  marked  in  Ireland,  both  in 
the  northern  and  in  the  southern  regions.  In  the  latter  the  Upper 
Old  Red  Sandstone,  which  may  be  roughly  described  as  represent- 
ing the  Welsh  or  Scotch  type,  is  always  unconformable  with  the 
underlying  rocks.  It  was  deposited  in  a  sheet  of  water  which  prob- 
ably covered  all  the  south  of  Ireland  from  near  Galway  Bay  to  the 
hills  of  Wicklow,  Wexford,  and  Carlow,  and  it  rests  in  places,  as  said 
above,  on  a  mass  of  unfossiliferous  grits  and  slates  higher  than  the 
Silurian.  Thus  it  seems  probable  that  Scotland  and  Ireland  were 
the  scene  in  the  Devonian  period  of  considerable  physical  disturb- 
ances, which  indeed  may  not  have  been  without  some  effect  even  in 
the  southwest  of  England.  All  the  evidence  at  our  command  indi- 
cates that  ordinary  marine  conditions  cannot  have  existed  north  of 
the  Bristol  Channel ;  though  possibly  South  Wales,  at  any  rate  for 
part  of  the  time,  may  have  been  covered  by  an  estuary  rather  than 
by  a  lake.  But  North  Wales,  the  Midland  counties,  and  most  of 
the  north  of  England  probably  formed  part  of  a  considerable  tract 
of  land,  for  here,  as  we  shall  find,  rocks  belonging  to  various  hori- 
zons in  the  Carboniferous  system  are  often  found  resting  upon 


THE  BUILDltfG  Of   TtfE  BRITISH  tSL£S. 


3*3 


deposits  which  are  not  newer,  at  any  rate,  than  the  top  of  the  Silu- 
rian. The  north  of  England  also  was  probably  the  scene  of  impor- 
tant movements  during  this  interval ;  but  the  sea  which  covered  the 
southwest  district  seems  to  have  extended  eastward  without  inter- 
ruption, for  Devonian  rocks  have  been  struck  in  borings  at  Turn- 
ford  and  in  Tottenham  Court  Road,  and  come  to  the  surface  from 
beneath  newer  rocks  between  Calais  and  Boulogne.  But  on  the 


FIG.   133.— RESTORATION  OF  THE  GEOGRAPHY  OF  BRITAIN  IN  EARLY  CARBONIFEROUS 
(LIMESTONE)  TIMES.     (After Jukes-Browne.} 

The  sea  is  indicated  by  horizontal  shading,  the  land  is  left  white. 

whole  a  large  part  of  Great  Britain  and  Ireland  in  the  Devonian 
period  must  have  been  above  the  surface  of  the  ocean. 

The  rocks  of  the  Carboniferous  system  at  the  outset  indicate  a 
contrast  of  conditions  somewhat  similar  to  those  afforded  by  the 
Devonian,  with,  however,  a  remarkable  difference.  In  both  there 
are  marine  deposits  in  the  south  and  fresh  water  in  the  north ;  but 
in  the  Devonian  the  former  occupy  a  small,  the  latter  a  large,  area, 


364  Fff£  STORY  Of  OUR  PLANET. 

while  in  the  Carboniferous  it  is  exactly  the  reverse.  The  lower  half 
of  the  Carboniferous  system,  wherever  it  is  found,  either  in  almost 
the  whole  of  England  or  in  Wales,  is  a  marine  deposit ;  but  on  both 
sides  of  the  southern  uplands  of  Scotland  it  is,  in  the  earlier  part, 
indubitably  fresh  water. 

The  Carboniferous  system  is  divided  into  three  great  groups — the 
Carboniferous  Limestone,  the  Millstone  Grit,  and  the  Coal  Meas- 
ures. These  vary  much  in  volume,  but  the  total  thickness  of  the 
system  is  often  ten  or  twelve  thousand  feet.  The  first  is  mainly  a 
marine  deposit,  the  second  and  third  are  mainly  fresh  water,  the 
evidence  in  either  case  being  conclusive.  But  a  detailed  study  of 
the  rocks  of  the  Carboniferous  system  in  various  parts  of  Britain 
throws  some  interesting  light  on  the  physical  geography  of  the 
period.  In  South  Wales  the  passage  from  the  Old  Red  Sandstone 
to  the  Carboniferous  Limestone  is  very  similar,  though  in  a  reverse 
order,  to  that  from  the  Silurian  to  the  Old  Red  Sandstone.  The  rocks 
in  the  former  case  lose  their  red  color,  and  pass  into  banded  shales 
and  limestones  containing  marine  fossils.  Presently,  after  about  150 
or  200  feet,  the  shales  disappear.  The  limestone  in  some  districts  on 
the  north  side  of  the  Bristol  Channel  is  often  about  2000  feet  thick, 
and  occasionally  more.  Then  it  is  replaced  by  banded  shales,  which 
are  followed  by  the  Millstone  Grit  and  the  Coal  Measures.  But  the 
sea  in  which  the  pure  limestone  was  deposited  was  evidently  limited 
in  area.  On  the  northern  margin  of  the  South  Wales  coal  field  the 
limestone  is  reduced  to  about  one-third  of  the  thickness  which  it 
has  on  the  opposite  side ;  it  attenuates  toward  the  Forest  of  Dean, 
losing  1900  feet  in  about  twenty-one  miles;  and  at  Newent,  in 
Gloucestershire,  it  is  gone,  and  the  Coal  Measures  rest  on  Lower 
Old  Red  Sandstone ;  it  also  thins  westward,  for  in  Pembrokeshire  it 
has  similarly  disappeared,  since  here  Coal  Measures  overlie  Ordovi- 
cian  rocks.  In  North  Devon  the  limestones  form  only  insignificant 
bands  in  a  great  mass  of  argillaceous  rocks,  while  in  South  Devon 
they  have  died  away.  North  of  these  places,  in  Eastern  Wales  and 
Western  England,  wherever  information  can  be  obtained,  the  lime- 
stones, as  far  as  the  neighborhood  of  the  Wrekin,  are  wanting,  and 
there  is  good  reason  to  believe  that  all  this  area  was  a  land  surface. 
Near  that  hill  and  on  the  north  of  Charnwood  Forest  they  set  in, 
and  thicken  out  northward,  very  rapidly  in  the  latter  case.  In  North 
Staffordshire  they  are  said  to  be  3000  feet  thick.  But  all  the  more 
northern  part  of  Wales  was  land,  for  in  the  Clwyd  valley  and  the  north 
of  Carnarvonshire  conglomerates  of  considerable  thickness  lie  at  the 


THE  BUII-D1NG  Of  THE  BRITISH  ISLES.  365 

base  of  the  limestone.  Perhaps  also  the  hill  region  of  Cumberland 
and  Westmoreland  formed  an  island  mass,  for  there  similar,  though 
thicker,  beds  of  conglomerate  occur.  The  sea — probably  again 
locally  interrupted  at  the  Isle  of  Man — extended  across  the  Channel 
to  Ireland,  and  by  far  the  larger  portion  of  that  country  must  have 
been  submerged,  for  the  limestones  in  places  attain  a  thickness  as 
great  as  in  any  part  of  England.  From  Dublin  to  Galway  Bay,  from 
Cork  Harbor  to  Donegal,  the  Carboniferous  Limestone  extends, 
even  now  mostly  in  an  uninterrupted  sheet.  Here  and  there  some 
small  island  may  have  risen  above  the  waves ;  the  old  continental 
land  may  have  lain  near  at  hand  on  the  west ;  but  probably  the  sub- 
mergence was  more  complete  than  in  any  of  the  earlier  periods  of 
geological  history. 

The  sea,  however,  over  the  English  area  was  not  only  interrupted 
in  the  Midlands  by  a  considerable  promontory  from  Wales,  or  by  a 
large  island  barely  separated  from  that  country,  but  was  limited 
toward  the  north.  As  the  Lower  Carboniferous  Measures  are  fol- 
lowed in  this  direction  from  South  Derbyshire,  not  only  do  the 
upper  shales  increase  rapidly  in  thickness,  but  also  the  limestones 
are  found  to  lose  their  purity,  and  to  be  split  up  by  intercalated  beds 
of  shale  and  sandstone.  At  last,  on  approaching  the  southern  border 
of  Scotland,  even  coal  seams  occur  on  the  horizon  of  the  Carbonif- 
erous Limestone,  and  at  its  base  is  a  considerable  thickness  of  strata 
(the  Tuedian),  to  which  a  fresh  water  origin  has  been  assigned. 
The  same  is  true  of  the  Carboniferous  system  in  the  central  valley 
of  Scotland  ;  for  an  indubitably  fresh  water  group,  containing  oil 
shales  and  some  coal,  with  thick  sandstones  and  even  calcareous 
shales  passing  locally  into  a  limestone,  underlies  the  equivalent  of 
the  Carboniferous  Limestone.  In  this  region,  however,  the  latter 
group  is  only  partially  marine.  There  is  but  little  pure  limestone, 
and  generally  even  that  is  thickly  interbanded  with  sedimentary 
materials  which  contain  some  important  seams  of  coal.  From  these 
considerations  it  seems  probable  that  even  the  thick  marine  lime- 
stones away  to  the  south  were  formed  in  a  sea  the  waters  of  which 
were  clear  rather  than  very  deep.  Probably  the  earlier  half  of  the 
Carboniferous  period  was  a  time  of  quiet  subsidence,  when  the 
border  district  of  the  old  continental  land  was  broken  up  into  island 
groups  and  its  larger  valleys  were  converted  into  fjords,  the  heads 
of  which  arrested  the  sand  and  mud  borne  down  by  the  rivers  which 
drained  the  more  mountainous  lands. 

At  last  a  change  occurred.     The  area  on  which  only  the  debris  of 


3&>  THE   STORY  6F  OUR  PLACET. 

organisms  had  accumulated  was  again  brought  everywhere  within 
the  reach  of  sediment,  and  the  Millstone  Grit  consists  of  detrital 
materials,  especially  of  sandstone.  So  the  rocks  continue  to  the  end 
of  the  period.  Beds  of  coal  are  intercalated  among  the  sediment, 
and  may  occur  even  in  the  Millstone  Grit ;  as  a  rule,  however,  they 
are  associated  with  the  lower  and  middle  part  of  the  Coal  Measures, 
especially  the  latter.  They,  of  course,  are  of  organic  origin.  The 
actual  coal  seams,  even  when  added  together,  do  not  amount  to  a 
very  great  thickness,  but  the  aggregate  of  the  sand  and  sandstones 
in  the  upper  part  of  the  Carboniferous  system  is  very  large,  perhaps 
sometimes  not  less  than  10,000  or  12,000  feet.  As  has  been  already 
said,*  these  beds  were  probably  formed  on  a  swampy  delta.  The 
sea,  however,  cannot  have  been  far  away,  for  at  two  or  three  horizons 
the  dark  muds  in  several  parts  of  England  contain  a  number  of 
marine  fossils.  This  lowland — probably  formed  by  a  group  of  con- 
fluent deltas,  as  on  the  northwest  of  the  Adriatic — covered  a  still 
larger  area  than  the  sea  by  which  it  was  preceded.  Land  which  had 
risen  above  the  latter  was  overwhelmed  by  the  sediment  and  over- 
grown by  the  coal  bog.  The  vast  plain  apparently  stretched  almost 
without  break  over  England.  Probably  it  was  only  imperfectly 
interrupted  by  the  southern  uplands  of  Scotland,  and  ran  up  to 
the  feet  of  the  Highlands  and  the  mountains  of  Donegal.  It  must 
have  extended  at  least  from  the  Welsh  border  over  almost  the 
whole  of  England,  for  beds  of  this  age  are  known  to  underlie  Burford, 
in  Oxfordshire,  and  coal  has  been  struck  full  1200  feet  from  the  sur- 
face at  Dover.  Similar  rocks  very  probably  extended  over  the 
greater  part  of  Ireland,  but,  unhappily  for  the  prosperity  of  that 
country,  the  coal  fields  are  now  few  and  scattered.  Time  and  Nature 
have  added  to  the  wrongs  of  Ireland  by  stripping  it  of  the  rocks 
which  might  have  been  a  source  of  material  wealth. 

Professor  Hull  pointed  out,  several  years  since,f  that  the  sedi- 
mentary materials  of  the  Carboniferous  system  exhibited  a  tend- 
ency to  become  thinner  in  the  northern  districts  toward  the  south- 
east or  south,  in  the  southwestern  districts  toward  the  east.  From 
these  facts  he  inferred  the  existence  at  that  period  of  sundry  large 
rivers — of  at  least  one  in  the  former  region  flowing  from  the  north- 
west or  north,  and  of  one  in  the  latter  flowing  from  the  west. 
There  may  have  been  yet  more,  but  such  masses  of  thick  and  wide- 
spread sediment  could  only  have  been  supplied  by  rivers  compared 

*  See  pp.  177-180. 

\QuarterlyJournalofthe  Geological  Society,  vol.  xviii.  1862,  p.    127. 


THE   BUILDING   OF   THE   BRITISH  ISLES.  367 

with  which  those  of  England  in  our  own  day  would  seem  little  more 
than  brooks. 

During  all  this  time  volcanic  outbursts  were  rare  and  local  *  in 
England,  but  they  continued  actively  in  Scotland.  The  region  of 
the  central  valley  must  have  been  dotted  over  with  cones  and 
craters  as  thick  as  the  uplands  of  Auvergne ;  the  majority  of  these 
ejected  basaltic  ashes  and  lava.  In  Arthur's  Seat,  on  the  shores  of 
the  Firth  of  Forth,  on  the  east  coast  of  Fife,  and  elsewhere,  the 
relics  of  these  ancient  volcanoes  may  be  studied  with  comparative 
ease.  They  had  begun  in  the  preceding  geological  period,  as  has 
been  said  above ;  they  continued  through  the  long  ages  of  disturb- 
ance and  denudation  which  introduced  the  Permian  period,  and  in  this 
theyseem  to  have  finallysputtered  themselves  out  and  becomeextinct. 

Much  controversy  has  arisen  among  geologists  as  to  the  relation 
of  the  Carboniferous  to  the  Permian  system.  In  some  countries  it 
is  hardly  possible  to  separate  them,  while  in  others  the  latter  seems 
severed  from  the  former  by  a  long  interval,  and  to  be  clearly  con- 
nected with  the  Trias.  In  England  the  evidence  is  conflicting, 
being  in  some  respects  favorable  to  one  view,  in  some  to  the  other. 
This,  however,  is  certain,  that  in  many  places  a  great  break  exists 
between  the  Carboniferous  and  the  Permian,  and  even  thousands  of 
feet  of  rock  were  removed  by  denudation  from  the  former  before 
the  lowest  beds  of  the  latter  system  were  deposited.  The  existence 
of  a  break  between  it  and  the  Trias  is  much  less  clearly  proved.  In 
the  north  of  England  Permian  beds  occur  on  both  sides  of  the  Pen- 
nine chain.  On  the  eastern  they  are  only  a  few  hundred  feet  in 
thickness,  and  consist  chiefly  of  limestones,  often  magnesian ;  f  on 
the  western  mainly  of  sandstones  and  shales,  the  calcareous  element 
being  comparatively  small.  The  strata  appear  to  attenuate  toward 
the  south,  and  were  limited,  in  the  opinion  of  Professor  Hull,  by 
a  barrier  which  extended  diagonally  across  the  plain  of  Cheshire. 
South  of  it  rocks  of  Permian  age  again  set  in,  though  they  are  not 
largely  exposed  at  the  surface.  In  this  region  they  consist  almost 
entirely  of  sandstones  and  marls,  with  some  breccias  and  conglom- 
erates. From  the  latter  it  is  clear  that  many  of  the  older  rocks  were 
being  denuded,  including  various  parts  of  the  Carboniferous  system, 

*  There  were  some  in  Devonshire,  and  occasional  discharges  of  lava  and  ashes  on  the 
bed  of  the  sea  in  Derbyshire. 

\  Some  of  which  makes  an  excellent  building  stone — used,  for  instance,  in  the  cathedral 
and  walls  of  York,  and  in  the  Jermyn  Street  Museum  and  the  Houses  of  Parliament,  the 
last-sometimes  being  of  an  inferior  quality. 


368  THE   STORY  OF  OUR  PLANET. 

even  down  to  the  limestones,  and  that  such  districts  as  the  Charn- 
wood  Hills  rose  well  above  water.  Professor  Hull  also  thinks  that 
the  Permian  rocks  of  the  Midlands  represent  only  the  deposits  of 
the  earlier  part  of  the  period,  and  are  anterior,  as  a  whole,  to  the 
limestones  of  the  northeast.  Probably  they  never  extended  much 
further  south  than  the  Malvern  Hills,  and  the  remainder  of  Eng- 
land in  this  direction  was  supposed  to  have  been  dry  land.  But  of 
late  years  it  has  been  maintained  that  a  great  mass  of  sandstones, 
breccias,  and  marls,  with  some  associated  volcanic  rocks,  which 
underlies  the  indubitable  Trias  of  Devonshire,  does  not  form  part, 
as  was  once  supposed,  of  that  system,  but  is  really  Permian,  and 
this  view  appears  now  to  be  meeting  with  general  acceptance. 

One  serious  difficulty  which  confronts  us  in  any  attempt  to  restore 
the  physical  geography  of  Britain  during  the  Permian  period  is  the 
date  of  the  uplift  which  formed  the  Pennine  Range.  By  some 
geologists  this  is  placed  between  the  Carboniferous  and  the  Permian  ; 
by  others  between  the  latter  and  the  Trias.  If  the  former  view  be 
correct,  the  sandy  beds  of  the  northwest  and  the  calcareous  beds 
of  the  northeast  must  have  been  deposited  in  separate  basins  ;  but 
in  the  other  case  they  might  have  been  parts  of  a  continuous  deposit, 
which  became  more  free  from  sediment  as  its  distance  from  the 
western  land  increased.  The  details  of  the  controversy  are  in  some 
respects  too  technical  for  discussion  in  these  pages,  so  that  we 
must  limit  ourselves  to  the  statement  of  certain  facts  concerning 
which  there  is  a  general  agreement. 

The  Carboniferous  period  was  closed  by  a  most  important  series 
of  earth  movements,  which  not  only  affected  the  whole  of  England, 
but  also  a  very  large  adjoining  area.  All  of  this  was  thrown  into  a 
series  of  anticlinal  and  synclinal  folds,  and  toward  the  south  a 
mountainous  mass  was  formed,  which,  even  if  we  do  not  apply  that 
term  to  anything  north  of  the  Bristol  Channel,  "  was  not  less  than 
300  miles  wide  across  the  strike  of  the  folds.  To  its  altitude  we 
have  no  clew,  but  its  breadth  must  have  exceeded  that  of  the  Alps, 
and  it  probably  extended  westward  beyond  the  southwestern 
angle  of  Ireland,  while  traces  of  it  can  be  followed  eastward  to 
beyond  the  Rhine — more  than  35°  of  longitude.  Yet  the  sea  now 
flows  where  some  of  its  highest  summits  may  have  risen  ;  its  only 
record  is  preserved  in  the  low  plateaus  and  comparatively  humble 
hills  of  Cornwall  and  Devon,  of  the  Channel  Islands  and  of  Brittany."* 

*  The  author,  Quarterly  Journal  of  the  Geological  Society,  vol.  xliii.  1887,  p.  320. 


THE  BUILDING   OF   THE  BRITISH  ISLES. 


369 


The  general  direction  of  the  folds  thus  produced  in  the  region  just 
mentioned  is  roughly  east  and  west,  but  in  the  northern  half  of 
England  they  trend  more  nearly  east-northeast. 

These  disturbances  cannot  but  have  affected  most  materially  the 
physical  geography  of  Britain.  They  probably  were  connected  with 
the  numerous  outbreaks  of  basaltic  and  other  volcanic  rock  in  many 
parts  of  England,  Scotland,  and  Ireland,  and  with  the  protrusion  of 


FIG.  134. — RESTORATION  OF  THE  GEOGRAPHY  OF  BRITAIN  IN  KEUPER  TIMES. 

(After  Jukes-Browne .) 
Water  and  land  as  in  Fig.  133. 

the  great  granitic  masses  in  Devon,  Cornwall,  and  Brittany.  These 
possibly  may  be  only  the  cores  of  ancient  volcanoes;  but  if  so,  the 
cones  which  once  crowned  the  hills  of  Dartmoor  must  have  been 
on  a  grand  scale.  Certain  it  is  that,  as  already  said,  the  Carbonif- 
erous rocks  in  some  places  were  largely  denuded  before  the  Per- 
mians  began  to  be  deposited. 
The  Permian  limestone  in  the  northern  area  contains  marine 


37°  THE   STORY  OF  OUR  PLANET. 

fossils ;  but  it  has  been  suggested  that  these  are  indicative,  not  so 
much  of  an  open  sea,  as  of  one  like  the  Baltic  or  even  the  Caspian. 
The  Triassic  deposits,  it  is  generally  agreed,  are  not  marine  in  origin. 
Gn  the  whole,  they  overlap  the  Permians,  but  the  break  between 
these  is  not  conspicuous.  This,  however,  is  clear — and  it  seems  a 
point  of  some  importance — that,  at  whatever  date  the  Pennine 
Range  was  upraised,  the  forces  which  brought  it  into  its  present 
form  must  have  acted,  roughly,  from  east  to  west,  or  at  an  angle  of 
from  70°  to  90°  with  those  which  produced  the  admittedly  pre- 
Permian  folds.  Movements,  however,  so  very  different  in  direction 
are  not  likely  to  have  been  consecutive,  but  were  probably  separa- 
ted by  a  long  interval  of  time.  Hence,  although  much  difference 
of  opinion  still  prevails,  and  the  earlier  date  of  the  Pennine  Range, 
perhaps,  finds  on  the  whole  more  favor,  I  incline  to  the  other  view, 
and  think  that  in  Permian  ages  a  sea  extended  across  the  northern 
part  of  England  from  east  to  west,  though  it  may  have  been  inter- 
rupted by  islands,  and  was  probably  shallow. 

The  Trias  in  England  is  generally  divided  into  two  groups,  called 
respectively  the  Bunter  and  the  Keuper ;  but  even  here  we  do  not 
escape  from  difficulties.  That  it  passes  up  gradually  into  the 
Jurassic  system  is  universally  admitted,  and  there  is  a  general  agree- 
ment as  to  the  circumstances  under  which  the  Keuper  was  formed. 
But  as  to  the  history  of  the  Bunter  much  controversy  still  prevails. 
This  group,  in  the  part  of  England  north  of  the  Malverns,  is  known 
to  exist  over  most  of  the  lowland  district  between  the  hills  of  Wales, 
of  the  Lake  District,  and  of  the  Pennines,  to  pass  round  the  south 
end  of  the  last  named,  and  to  follow  their  eastern  flank  to  the  neigh- 
borhood of  the  Tees.*  On  this  side  probably  it  does  not  extend  so 
far  east  as  the  coast  of  North  Lincolnshire,  but  occupies  a  kind  of 
channel  between  the  Pennine  Hills  and  some  rising  ground  (now 
concealed  beneath  newer  rocks) ;  it  hardly  does  more  than  reach 
Leicestershire,  Warwickshire,  and  the  middle  of  Worcestershire. 
On  the  western  side  of  this  region  the  Bunter  consists  of  two  wedge- 
like  masses  of  sand  parted  by  a  similarly  shaped  bed  of  pebbles,  which 
generally  extends  slightly  beyond  the  other  two.  The  pebble  bed, 
however,  is  split  up  by  thin  bands  of  sandstone,  and  becomes  more 
arenaceous  in  the  neighborhood  of  the  Irish  Channel.  The  Bunter 
group  as  a  whole  attains  to  a  considerable  thickness.  In  parts  of 

*  There  is  some  Trias  on  the  southern  and  western  margins  of  the  Lake  District,  as 
well  as  near  Carlisle  ;  but  as  the  amount  is  comparatively  small,  and  geologists  are  not  in 
accord  as  to  its  correlation,  we  must  abstain  from  discussing  it. 


THE  BUILDING  OF   THE  BRITISH  ISLES.  371 

Cheshire  and  Lancashire  this  varies  from  one  to  two  thousand  feet, 
and  in  Staffordshire  the  pebble  bed  alone  is  often  three  or  four  hun- 
dred feet  thick.  In  any  attempt  to  unravel  the  history  of  this  group 
two  questions  present  themselves  for  settlement — namely,  how  the 
materials  were  transported,  and  whence  they  were  derived.  It  is 
generally  admitted  that  the  Bunter  deposits  are  not  likely  to  be  of 
marine  origin ;  they  are  quite  without  fossils,*  and  much  resemble 
the  pebble  beds  of  Oligocene  age  in  Switzerland  (called  Nagelflu/i), 
which  are  known  to  be  fresh  water.  They  have  also  a  considerable 
resemblance  to  the  coarse  gravels  which  coverall  the  lowlands  around 
the  Alps.  It  is,  however,  uncertain  whether  they  should  be  consid- 
ered lacustrine  deposits,  or  distinctly  fluviatile,  like  the  last-named 
gravels.  Speaking  for  myself,  I  find  the  tripartite  arrangement  very 
difficult  to  explain  on  any  other  hypothesis  than  that  these  wedge- 
like  masses  are  true  river  deposits,  the  produce  of  streams  which 
first  increased  and  then  again  decreased  in  velocity.  That  these 
were  broad  and  important  is  indicated  by  the  volume  of  the  deposit, 
and  that  the  average  rate  of  the  current  was  from  two  to  three  miles 
an  hour  is  proved  by  the  size  of  the  pebbles. 

But  from  what  region  have  these  traveled  ?  To  this  question  also 
different  answers  are  returned,  but  the  following  are  the  principal 
facts  of  which  account  must  be  taken  in  framing  an  hypothesis  :  The 
Bunter  beds  consist  partly  of  sandstone  (composed  chiefly  of  quartz, 
with  occasionally  mica  and  felspar),  partly  of  pebbles.  The  sandstone, 
on  careful  study,  indicates  that  it  has  been  formed  by  the  destruc- 
tion of  a  large  mass  either  of  granitoid  rock  or  of  some  older  sand- 
stone. Its  volume,  on  a  rough  approximation,  is  equal  to  that  of 
an  unbroken  range  of  hills  65  miles  long,  4  miles  wide,  and  5000 
feet  high.  Even  the  pebbles  probably  represent  a  mass  of  rock 
equal  to  four  cubic  miles,  or  a  similar  chain  of  hills  20  miles  long, 
2  miles  wide,  and  1000  feet  high.f  It  is  therefore  evident  that, 
whether  the  sandstones  were  derived  from  older  sandstones  and  the 
pebble  beds  from  more  ancient  conglomerates,  or  whether  both  were 
obtained  directly  from  the  parent  rocks,  they  represent  the  debris  of 
a  large  land  area,  the  produce  of  great  and  powerful  streams.  Such 
deposits  cannot  be  furnished  by  miles  of  reefs  and  skerries  or  by 

*  Some  of  the  pebbles  contain  fossils,  but  these,  of  course,  belong  to  rocks  of  an  earlier 
date.  So  far  as  the  writer  is  aware,  no  contemporaneous  fossils  have  been  found  in  the 
Bunter  beds  of  the  northern  half  of  England. 

f  The  author,   Presidential  Address  to  Section    C,   British  Association,   Birmingham, 

1886. 


372  THE   STORY  OF  OUR  PLANET. 

chains  of  islands  moderate  in  size  and  elevation  —  that  may  be 
regarded  as  a  certainty  if  geological  principles  have  any  value.  Let 
us,  then,  turn  for  a  moment  to  the  pebbles  to  see  what  further  light 
they  can  throw  on  the  question.  A  limited  number  consist  of 
Palaeozoic  rocks,  ranging  upward  from  the  Ordovician  or  Cambrian  ; 
not  a  few  are  vein-quartz.  This  group  gives  little  help — such  a 
rock,  for  instance,  as  a  chert,  of  Carboniferous  Limestone  age,  may 
have  come  from  any  quarter  of  the  compass.  One  variety,  how- 
ever, affords  some  hope  of  discovering  its  place  of  origin.  It  is  a 
hard  grit  or  quartzite,  containing  organic  remains,  which  resembles 
a  fossiliferous  rock  at  the  Lickey  Hills  and  certain  pebbles  in  a  con- 
glomerate (of  about  the  same  age)  at  Budleigh  Salterton,  in  Devon- 
shire. But  though  these  pebbles  are  far  from  common,  the  former 
area  seems  too  limited  in  extent  to  have  been  the  center  of  a  dis- 
persion which  has  been  traced  at  least  as  far  as  the  neighborhood  of 
Nottingham,  and  the  latter  seems  excluded  by  the  fact  that  at  this 
epoch  the  northern  and  southern  districts  appear  to  have  been  sep- 
arated by  a  neck  of  land.  So  none  of  these  pebbles  furnish  evidence 
of  any  value  ;  but  still  a  considerable  number  of  others  have  been 
identified.  One  of  the  commonest  rocks  in  the  pebble  bed  is  a 
quartzite,  so  compact  and  hard  as  to  break  sometimes  with  almost 
a  smooth  surface.  It  is  occasionally  liver-colored,  not  seldom  red- 
dish, more  commonly  various  shades  of  gray,  from  almost  white  to 
dark.  This  quartzite  does  not  present  mere  thar.  a  superficial 
resemblance  to  any  of  those  known  to  occur  in  England  or  Wales, 
such  as  the  rock  at  Hartshill,  the  Wrekin,  the  Lickey,  or  the  Stiper 
Stones,  but  it  is  exactly  like  the  great  mass  of  basement  Cambrian 
quartzite  which  is  so  conspicuous  a  feature  in  the  scenery  of  the 
Northwest.  Highlands — a  rock  which  indubitably  has  furnished 
myriads  of  pebbles  to  the  conglomerates  of  Old  Red  Sandstone  and 
early  Carboniferous  age  in  Scotland.  Besides  this  quartzite,  pebbles 
occur  of  a  peculiar  hard  quartz-felspar  grit,  which  often  might  be 
mistaken  for  a  granite.  No  such  rock  can  be  found  above  the  surface 
anywhere  in  England  or  in  Wales,  but  it  exactly  corresponds  with 
the  Torridon  Sandstone  of  the  Northwest  Highlands,  which  also 
occurs  in  the  above-named  Scotch  conglomerates.  Again,  pebbles 
of  rather  compact  igneous  rocks,  mostly  varieties  of  felstone,  are 
far  from  rare  in  this  Bunter  deposit.  These,  as  a  rule,  differ  from 
any  felstone  known  either  in  Wales  or  in  England,*  but  they  closely 

*  Some  of  the  Cornish  rocks  present  the  nearest  resemblance  to  these,  but  the   likeness 
is  not  strong  ;  this  area,  as  stated  above,  cannot  have  supplied  materials. 


THE  BUILDING  OF    THE   BRITISH  ISLES.  373 

resemble  the  felstones  which,  as  already  said,  are  so  abundant  in  the 
hill  regions  of  Scotland,  and  were  mostly  erupted  in  Old  Red  Sand- 
stone times.  They  also  are  very  common  in  the  above-named 
Scotch  conglomerates. 

The  wedge-like  shape  of  the  Bunter  deposits,  with  their  thick 
ends  pointing  to  the  northwest  or  north,  indicates  that  the  materials 
have  traveled  from  that  direction.  Here,  however,  a  difficulty  is 
raised,  for  the  pebble  beds  in  the  neighborhood  of  the  Mersey, 
though  more  than  twice  as  thick  as  they  are  in  Staffordshire,  not 
only  are  much  more  sandy,  but  also  the  pebbles  themselves  run  dis- 
tinctly smaller.  We  might  have  expected,  it  is  urged,  that  the 
materials  would  have  become  coarser  in  approaching  the  source  from 
which  they  were  supplied.  This,  no  doubt,  is  a  real  difficulty,  and 
it  has  so  much  weight  with  some  geologists  that  they  maintain  the 
general  drift  of  the  materials  to  have  been  from  the  south  or  the 
east.  But  at  the  present  time  no  rocks  of  the  required  kinds  can  be 
found  in  either  of  these  directions  ;  and  when  advocates  of  these 
hypotheses  fall  back,  in  order  to  support  them,  on  ridges  which  they 
assume  to  be  buried  beneath  later  sediments,  we  may  reply  that  our 
knowledge  of  the  physical  geography  of  the  district  to  the  south 
enables  us  to  affirm  that  any  high  ground  in  that  quarter  must  have 
been  far  too  restricted  in  area  to  have  supplied  the  requisite  quantity 
of  materials,  and  that  not  only  is  there  no  evidence  of  the  existence 
in  early  Secondary  times  of  any  land  in  the  east  capable  of  feeding 
large  rivers  and  supplying  huge  masses  of  sand  and  gravel,  but  also 
all  that  is  known  is  opposed  to  the  idea.  We  find,  however,  both  in 
later  Primary  and  in  earlier  Secondary  times,  distinct  evidence  that 
a  continental  land  once  existed  in  the  northwest,  and  that  materials 
drifted  from  this  quarter.  Seeing,  then,  that  the  argument  founded 
on  the  size  of  the  pebbles  is  directly  contradicted  by  that  resting  on 
the  northern  thickening  of  the  deposits,  these  may  be  dismissed  as 
mutually  destructive,  and  the  hypothesis  of  a  northern  derivation  is 
left  in  possession  of  the  field.* 

The  sands  and  sandstones  of  the  Bunter  group  are  often  false- 
bedded,  and  occasionally  contain  well-rolled  grains  in  considerable 
abundance,  the  latter  being  indicative  of  the  action  of  wirid.f  We 

*  It  must  not  be  forgotten  that  rivers  have  a  tendency  to  bifurcate  and  spread  out  in  the 
area  of  their  deltas  ;  thus  the  distribution  of  pebbles  may  have  been  more  general  in  the 
Midland  area,  and  may  have  been  limited  to  a  few  main  channels  (which  have  not  yet  been 
struck)  in  the  more  northern  one.  Here  the  sand  would  be  mainly  a  flood-time  product. 

f  See  P.  85. 


374  THE   STORY  OF  OUR  PLANET. 

may  picture  to  ourselves  a  highland  or  mountainous  region,  like 
another  Scandinavia,  rising  on  the  west  and  northwest  of  the  British 
Isles.  From  the  portals  of  its  hills  issued  full-flowing  rivers,  laden 
with  sand  and  pebbles,  which  were  deposited  on  the  lowlands,  as 
they  have  been,  and  still  are,  spread  out  at  the  foot  of  the  Alps. 
On  this  mountain  region  the  rainfall  may  have  been  heavy  ;  but  the 
frequency  of  the  wind-worn  grains  and  the  wide  extension  of  the 
sands  suggest  that  the  plains  may  have  been  arid  and  barren.  What 
became  of  these  rivers  we  cannot  yet  say.  They  may  have  lost 
themselves  in  deserts,  like  some  rivers  at  the  present  time  ;  but  it  is 
more  probable  that  their  waters  passed  out  through  some  compara- 
tively narrow  channel,  now  hidden  under  the  southern  part  of  Eng- 
land, to  join  a  sea  which  at  this  time  covered  a  portion  of  Central 
Europe.* 

In  the  present  state  of  our  knowledge  it  is  difficult  to  say  much 
about  the  Bunter  deposits  of  the  southwest  of  England.  If  the 
above-named  breccias,  sandstones,  and  marls  really  belong  to  the 
Permian  period,  the  pebble  bed  already  mentioned  as  occurring  at 
Budleigh  Salterton,  which  does  not  exceed  150  feet  in  thickness, 
and  is  usually  less  than  100  feet,  is  almost  the  sole  representative  of 
the  group  in  question.  In  this  bed  well-rounded  pebbles  of  quartz- 
ite  or  hard  grit  are  common,  which  contain  fossils.  Of  these  the 
majority  have  been  assigned  f  to  Lower  Devonian  rocks,  and  the 
remainder  in  part  to  the  Bala,  in  part  to  the.Arenig.  Such  rocks 
occur  more  or  less  commonly  in  Devonshire,  Cornwall,  and  north- 
western France,  so  that  these  pebbles  were  probably  brought  by 
streams  which  flowed  from  the  west  or  southwest — that  is  to  say, 
from  a  prolongation  in  the  direction  of  Armorica  of  the  great  land 
area  which  has  been  already  mentioned. 

The  Keuper  group  consists  of  sandstones  of  moderate  thickness, 
followed  by  a  great  mass  of  marls  or  clays.  The  former  vary  from 
alternating  layers  of  sandstones  and  marls  to  good  solid  sandstones, 
which  are  excellent  for  building.  The  marls  are  red  in  color,  with 
greenish-gray  bandings ;  they  are  locally  interrupted  by  thin  sand- 
stones, and  in  the  south  of  England  by  breccias.  The  last  named 
are  found  at  different  elevations  encircling  the  hilly  districts,  such 
as  the  Mendips,  and  are  composed  of  fragments  from  their  materials, 

*  It  is  commonly  admitted  by  geologists  that  the  general  direction  of  the  drainage  for 
a  considerable  time  immediately  after  the  Trias  was  in  this  direction. 

f  By  the  late  Dr.  T.  Davidson,  "  Monograph  of  British  Fossil  Brachiopoda,"  vol.  iv. 
P-  337- 


THE  BUILDING   OF   THE  BRITISH  ISLES. 


375 


generally  Carboniferous  Limestone,  which  has  often  become  dol- 
omitic.  Evidently  these  are  shore  deposits,  formed  in  compara- 
tively quiet  water.  Ripple  marks,  sun  cracks,  and  rain  prints  are  not 
unfrequent  in  certain  of  the  sandstones  ;  the  footprints  also  and 
bones  of  saurians  and  amphibians, 
with  the  remains  of  fishes  and  of 
plants,  are  found,  though  they 
are  not  common.  The  marl  is 
almost  unfossiliferous,  though  the 
breccias  have  produced  a  few 
relics  of  interest,  but  it  frequently 
contains  gypsum  and  rock  salt  or 
brine.*  Occasionally  a  slight  un- 
conformity may  be  detected  at  the 
base  of  the  Keuper,  and  a  marine 
deposit  f  is  intercalated  in  Eastern 
France  and  in  Germany  between 
it  and  the  Bunter,  which,  however, 
is  not  represented  either  in  Eng- 
land or  in  the  northern  part  of 
France.  The  lower  part  of  the 
Keuper  seems  to  indicate  a  con- 
tinuance of  conditions  generally 
resembling  those  which  prevailed 
in  the  Bunter,  but  the  marls  with 
their  gypsum  and  rock  salt  are 
similar  to  the  deposits  of  an  in- 
land sea.  That  the  Keuper  marls 
were  formed  under  such  condi- 
tions is  now  regarded  as  beyond 
doubt.  At  that  epoch  a  large  in- 
land sea  must  have  covered  a  con- 
siderable part  of  England — in 
shape  something  like  the  letter  Y. 
The  arms  were  parted  by  the  Pen- 
nine Hills;  on  one  these  formed 
the  western  shore,  the  eastern  limit 
being  rising  ground  in  the  direc- 

*  No  mollusca  have  been  found,  but  the  cases  of  a  few  small  Crustacea  (Estheria),  which 
are  commonly  fresh  water,  occur  locally. 

f  Called  the  Muschelkalk.     (See  the  next  chapter.) 


FIG.  135.— SUN  CRACKS  AND  FOOT- 
PRINTS (CHEIROTHERIUM),  TRIAS, 
HESSBERG  (THURINGIA). 

The  hind  feet  larger  than  the  fore,  and  more  than 
one  animal  has  left  its  mark. 


376  THE   STORY  OF  OUR  PLANET. 

tion  of  the  German  Ocean  ;  the  western  arm  passed  between  the 
Cambrian  and  Cumbrian  Hills,  in  the  direction  of  the  Irish  Sea,  at 
least  to  Antrim.  This  huge  salt  lake  in  many  places,  at  any  rate 
during  part  of  the  time,  must  have  been  studded  with  groups  of 
islands.*  The  Mendip  Hills,  the  Quantocks,  and  many  other  undu- 
lating masses  in  Somersetshire  and  the  neighborhood  rose  above 
its  surface,  as  the  Steep  Holm  and  other  islands  now  interrupt  the 
Bristol  Channel.  If  we  would  form  a  picture  of  this  region  in  the 
Keuper  age,  we  have  only  to. broaden  the  area  of  the  Severn  Sea, 
as  it  appears  sometimes  even  now,  when, 

Tis  water  here  and  water  there, 

And  the  lordly  Parret's  way 
Hath  never  a  trace  on  its  pathless  face 

As  in  the  former  clay. 

The  salt  lake  at  one  time  must  have  covered  much  of  the  lower 
ground  in  this  part  of  England,  between  the  uplands  of  Cornwall, 
Devonshire,  and  South  Wales.  Its  western  shore  was  doubtless 
formed  by  the  hills  of  Wales,  while  on  the  east  it  was  probably 
bounded  by  an  upland  region,  now  underlying  Middlesex,  Essex, 
and  the  adjoining  districts,  to  which  we  shall  again  refer.  In  the 
Midlands  the  hills  of  Charnwood  Forest,  at  least  for  a  considerable 
part  of  the  period,  formed  a  lonely  island  group,  for  here  in  many 
places  the  marls  can  be  seen  resting  upon  the  rugged  surface  of  the 
old  land,  where  they  have  filled  up  inequalities  and  glens.  They 
often  contain  blocks  of  stone,  which  lay  loose  on  the  surface  myri- 
ads of  years  ago,  just  as  these  are  still  scattered  on  any  mountain 
side.  Triassic  deposits  also  occur  on  the  western  shore  of  Scotland, 
and  in  the  neighborhood  of  the  Moray  Firth.  The  map  on  p.  369, 
a  reduction  of  one  made  by  Mr.  Jukes-Browne,  gives  a  general  idea 
of  the  area  which  must  have  been  occupied  by  this  great  salt  lake, 
and  of  the  probable  connection  of  these  northern  outliers  with  the 
principal  sheet  of  water.f 

Into  this  lake,  doubtless,  the  rivers  already  mentioned,  with  all 
the  streams,  great  and  small,  from  the  borderland,  discharged  their 
waters.  Any  coarse  material,  as  is  usual  in  lakes,  would  be  depos- 
ited in  the  immediate  neighborhood  of  the  shore ;  only  the  finer 
mud  would  float  for  any  distance  before  it  sank  to  the  bottom.  So 

*  See  a  map  by  Professor  I.loycl  Morgan,  published  in  Mr.  Jukes- Browne's  "  Building 
of  the  British  Isles,"  ch.  viii. 

f  A.  J.  Jukes-Browne,  "  Building  of  the  British  Isles,"  ch.  viii. 


THE   BUILDING   OF    THE  BltlTISH  ISLES.  377 

the  Keuper  clay,  as  might  be  expected,  is  generally  very  uniform  in 
character.  From  Antrim  to  Devonshire  specimens  might  be  col- 
lected so  similar  that  they  would  be  practically  indistinguishable. 
At  present  the  exact  position  of  the  barrierwhich  toward  the  south- 
east separated  this  salt  lake  from  the  sea  cannot  be  ascertained  with 
precision.  Probably  it  was  comparatively  low,  for  no  marked  dis- 
turbances appear  to  have  accompanied  the  return  of  marine 
conditions. 

The  Keuper  deposits  in  the  region  of  the  Eastern  Alps  are  dis- 
tinctly marine,  and  they  are  succeeded  by  an  important  mass  of 
strata,  often  2000  feet  thick,  of  like  origin,  which  is  named  Rhaetic, 
and  is  sometimes  treated  as  a  separate  system.  The  Keuper,  in 
many  parts  of  England,  also  passes  up  into  beds  which  contain 
fossils  and  are  evidently  of  this  age ;  but  these  are  very  thin,  com- 
monly not  exceeding  30  or  40  feet.  The  two  groups  are  not  sharply 
separated.  The  Keuper  loses  its  distinctive  color — becomes  first 
gray  and  then  dark — and  the  characteristic  Rhaetic  fossils  make  their 
appearance.  So  these  beds  in  England  are  not  generally  treated  as 
a  separate  system,  but  are  grouped  with  the  Trias.  There  can  be 
little  doubt  that  the  sea  gradually  overflowed  the  barrier,  and  opened 
a  communication  with  the  salt  lake.  The  waters  of  the  latter  prob- 
ably— as  is  usual  in  such  cases — were  almost,  if  not  quite,  lifeless  ; 
but  now  by  degrees  their  saltness  would  be  reduced,  and  they  would 
become  habitable,  and  be  invaded  by  organisms  from  the  outer  sea. 
But  by  this  time  the  Rhaetic  fauna  itself  was  becoming  enfeebled  ; 
and  no  very  long  time  after  the  sea  once  more  ebbed  and  flowed 
over  parts  of  the  British  Isles,  this  addition  to  its  domain  was 
invaded  by  the  young  and  vigorous  fauna  of  the  coming  Jurassic 
period.  All  through  the  remainder  of  the  Secondary  era  we  shall 
find  the  march  of  life  to  have  been  from  the  southeast.  The  Norman 
and  the  Saxon  did  but  follow  a  path  which  had  been  trodden  by  the 
animal  creation  long  ages  before  man  had  appeared  upon  the  globe, 
for  even  in  these  distant  times  the  British  seas  were  always  peopled 
by  colonists  from  France  and  from  Germany. 

The  Jurassic  system  in  Britain  is  generally  subdivided  into  the 
Lias  and  the  Oolites.  The  former  is  a  mere  patois  word  adopted 
into  science  ;  the  latter  denotes  a  peculiarity  in  some  of  the  lime- 
stones, which  are  made  up  of  small  rounded  grains  like  the  "  hard- 
roe  "  of  a  herring.  They  are  equally  objectionable,  but  have  to  be 
tolerated.  Both  the  Lias  and  the  OoVites  are  divided  into  a  Lower, 
Middle,  and  Upper.  The  beds  vary  considerably  in  mineral  char- 


378  THE   STORY  OF  OUR  PLANET. 

acter  and  in  thickness — perhaps  about  2500  feet  may  be  taken  as  a 
rough  average  approximation.  Jurassic  rocks  stretch  from  the  coast 
of  Dorset  diagonally  across  England  to  Yorkshire,  but  only  one  or 
two  fragmental  patches  of  Lias  indicate  the  extension  of  an  arm  of 
the  sea  toward  the  northwest.  Here,  however,  much  has  been 
removed  by  subsequent  denudation,  so  that  we  may  fairly  assume 
that  the  sea,  like  the  preceding  salt  lake,  extended  at  least  as  far  as 
Antrim.  At  first  sight  it  might  be  supposed  that  the  Jurassic  rocks 
indicated  conditions  of  deposit  extremely  diverse,  but  a  further  study 
leads  to  the  conclusion  that,  on  the  whole,  they  are  very  closely  con- 
nected. The  rocks  are  sandstones,  clays,  and  limestones;  the  first, 
as  a  rule,  being  rather  limited  in  extent  and  thickness.  Putting 
them  aside,  and  regarding  the  Jurassic  system  of  Britain  as  a  whole, 
we  find  it  to  consist  of  three  great  masses  of  clay,  followed  in  each 
case  by  a  zone  in  which,  though  some  interesting  variations  occur, 
limestones  dominate.  These  clays  are  the  Lias  (regarded  as  a  single 
deposit),  the  Oxford  Clay,  and  the  Kimeridge  Clay.*  To  the  first 
of  them  succeed  the  Lower  or  Bath  Oolites ;  to  the  second,  the 
Oxford  Oolites  ;  to  the  third,  the  Portland  Oolites.  Of  these  three 
clays  the  Lias  obviously  was  deposited  as  a  whole  at  no  great  dis- 
tance from  land.  Fronds  of  ferns,  leaves  of  plants,  and  pieces  of 
wood  are  not  rare  ;  a  few  land  shells  have  been  found  in  deposits  of 
this  age  in  Somersetshire ;  insects  are  not  very  uncommon  in  some 
localities.  It  becomes  sometimes  sandy,  sometimes  calcareous.  A 
sea — the  outlines  of  which  probably  corresponded  roughly  with 
those  of  the  Keuper  Lake — received  very  similar  materials  f  from 
the  same  sources.  The  same  is  probably  true  of  the  Oxford  Clay 
and  the  Kimeridge  Clay,  though  indications  of  the  proximity  of  land 
are  not  so  frequent  or  so  marked.  Very  likely  these  dark  clays  were 
partly  supplied  from  the  shales  of  the  Carboniferous  system,  for  in 
the  Pennine  Hills  and  other  parts  of  Britain  its  rocks  must  have 
undergone  much  denudation  during  this  period. 

The  Lower  Oolites  are  not  nearly  so  thick  as  the  Lias,  and  are 
very  variable  ;  this  remark  also  holds  good  of  the  remainder  of  the 
Jurassic  system.  Important  limestones  occur  in  the  southwest  of 
England,  as  in  Somersetshire  and  Gloucestershire,  and  in  the  north- 

*  The  second  and  the  third  may  be  roughly  estimated  at  about  500  feet  in  thickness  ; 
the  first  is  sometimes  more  than  twice  this  amount. 

\  The  Lias  clay  is  generally  dark  colored,  and  the  Keuper  red,  but  this  difference  is  only 
due  to  the  exceptional  circumstances  under  which  the  latter  was  deposited,  and  docs  not 
indicate  a  real  difference  of  dctrital  material. 


THE  BUILDING  OF  THE   BRITISH  ISLES.  379 

east,  as  in  Lincolnshire.  In  the  former  district  two  such  beds 
exist — that  quarried,  for  example,  near  Cheltenham,  and  that  all 
about  the  town  of  Bath.  In  the  latter  we  find  one,  that  called  the 
"  Lincolnshire  Limestone."  All  these  generally  are  very  fine  lime- 
stones, composed  almost  wholly,  directly  or  indirectly,  of  organic 
remains.  The  other  beds  in  this  group  are  varied  in  character,  and 
indicate  deposits  in  shallower  water,  and  occasionally  estuarine  con- 
ditions. These  seem  to  have  been  almost  permanent  in  Yorkshire, 
for  plant  remains  are  often  abundant,  and  even  thin  seams  of  coal 
occur.  The  "  Cheltenham  "  Limestone  gradually  disappears  as  it  is 
traced  to  the  northeast,  and  in  south  Northamptonshire  its  position 
is  marked  by  a  slight  unconformity,  but  in  the  north  of  the  county 
the  "  Lincolnshire"  Limestone  comes  in  at  this  horizon,  and  attains, 
after  a  time,  a  thickness  of  seventy  to  eighty  feet,  again  thinning 
so  as  to  be  very  feebly  represented  in  Yorkshire.  The  "  Bath  " 
Oolite  is  more  persistent,  but  in  the  Midland  and  northern  counties 
it  is  reduced  to  a  bed  only  a  dozen  or  twenty  feet  thick,  which  is  of 
little  or  no  value  to  the  quarryman.  It  is  therefore  evident  that  the 
land  must  have  been  very  near  to  the  north  of  Yorkshire. 

The  Oxford  Oolites  indicate  a  recurrence  of  similar  conditions. 
Limestones  extend  from  Dorsetshire  to  Oxfordshire,  in  which  county 
they  cease  rather  abruptly,  and  the  clay  underlying  them  passes  on 
till  it  graduates  upward  into  the  Kimeridge  Clay.  Except  for  a 
little  insulated  patch  of  limestone,  obviously  an  old  coral  reef,  which 
occurs  between  Cambridge  and  Ely,*  this  continuous  mass  of  clay 
extends  from  North  Oxfordshire  to  South  Yorkshire,  where  lime- 
stones are  again  found. 

In  Dorsetshire  the  Kimeridge  Clay  is  succeeded  by  the  Portland 
Limestone,f  which  may  be  traced  to  Buckinghamshire.  North  of 
this  county  for  a  considerable  distance  a  break  exists  in  the  record, 
the  result  of  an  ancient  denudation.  In  Yorkshire,  however,  the 
Kimeridge  Clay  passes  upward  into  one  which  contains  a  few  fossils 
of  Portlandian  age,  and  clays  continue  till  we  reach  the  base  of  the 
Cretaceous  system.  The  Portland  strata  in  the  south  of  England 
are  succeeded  by  estuarine  and  fresh  water  deposits,  called  the  Pur- 
beck  group.  These  indicate  a  river  delta,  and  show  that  the  land 
had  risen.  In  some  places  an  old  soil,  containing  the  stems  of  coni- 
fers and  the  stools  of  cycads,  can  be  found,  which  is  a  remnant  of  an 

*  At  Upware  in  the  Fens,  on  the  right  bank  of  the  Cam. 

f  In  this  county  a  bed  of  sand  lies  between  it  and  the  Kimeridge  Clay,  but  the  group 
exhibits  much  variation. 


38o 


THE   STORY  Of  OUR  PLANET. 


actual  land  surface.  The  river  delta  may  be  perhaps  traced  into 
Buckinghamshire,  north  of  which  it,  like  the  Portland  Limestone, 
is  lost. 

A  number  of  deep  borings  have  been  made  in  the  southeastern 
counties  which  throw  much  light  on  the  geography  of  Britain  dur- 
ing the  Jurassic  epoch.  At  Netherfield,  near  Battle  (north  of  Hast- 


FIG.    136. — MAP  OF  DEEP  BORINGS  IN  THE  SOUTHEAST  OF  ENGLAND  (Whitaker). 

The  figures  give  the  distance  in  miles  (the  Streatham  and  Dover  borings  have  been  com- 
pleted since  the  map  was  made  ;  the  arrow  points  to  the  position  of  the  latter). 

ings),  after  going  through  Purbeck  strata  and  some  sandy  beds  rep- 
resenting the  Portland,  the  Kimeridge  Clay  was  traversed,  followed 
by  a  representative  of  the  Oxford  Oolites  (mostly  clayey),  and  then 
the  boring  was  abandoned,  at  a  depth  of  about  1900  feet  from  the 
surface,  while  it  was  still  in  the  Oxford  Clay.  This  spot,  therefore, 
indicates  a  point  in  the  channel  along  which  the  finer  sediment  was 
discharged  by  the  "  main  sewer  "  of  England  in  Jurassic  times.  At 
Chatham  Oxford  Clay  was  pierced,  but  all  the  overlying  Jurassic 


THE   BUILDING   OF    THE  BRITISH  ISLES.  381 

rocks  were  missing.  In  the  borings  at  Streatham,  Richmond,  Tot- 
tenham Court  Road,  Kentish  Town,  Crossness,  Turnford,  Ware, 
and  Harwich  various  Palaeozoic  rocks  were  struck  beneath  the  bot- 
tom beds  of  the  Cretaceous  system,  at  depths  of  from  800  to  iioo 
feet.  In  all  these  deposits  of  Neocomian  age  were  either  wanting 
or  very  thin.  In  most  cases  Jurassic  rocks  were  also  absent,  but  at 
Tottenham  Court  Road,  Richmond,  and  Streatham  a  very  moderate 
thickness  (less  than  90  feet)  of  Jurassic  rock  was  found,  which  is 
referred  to  the  age  of  the  Bath  Oolites.  Two  inferences  follow  from 
these  facts:  one,  that  the  Jurassic  sea  was  bounded  on  the  east  by 
a  considerable  mass  of  land  which  lay  beneath  the  lower  part  of  the 
present  valley  of  the  Thames,  and  extended  for  some  distance  north- 
ward (Chatham,  probably,  is  situated  over  its  southern  slope,  and 
Hastings  above  the  channel  which  separated  it  from  the  western 
land) ;  the  other,  that  the  most  marked  submergence  in  Jurassic 
times  was  during  the  Lower  Oolite  and  contemporaneous  with  the 
deposition  of  the  Bath  Limestone. 

We  may  therefore  conclude  that  a  downward  movement  contin- 
ued throughout  the  greater  part  of  the  Jurassic  period,  the  rate  of 
which,  however,  was  probably  not  quite  uniform.  Each  of  the 
limestones  may  indicate  a  time  of  slightly  more  rapid  depression, 
when  the  sea  would  invade  the  valleys  and  convert  them  into  fjords, 
at  the  head  of  which  the  mud  brought  by  the  river  would  be  depos- 
ited. These,  by  degrees,  would  be  filled  up  and  become  low  plains, 
till  at  last  the  rivers  once  more  emptied  themselves  directly  into 
the  sea,  and  their  mud  was  drifted  away  by  tidal  and  other  currents. 
The  same  result  might  also  be  produced  by  slight  movements  in  an 
opposite  direction.  If,  at  the  end  of  a  time  when  limestone  had 
been  forming,  an  elevation  of  a  few  yards  were  to  occur,  a  fjord 
would  be  replaced  by  dry  land,  and  the  river  as  it  hurried  through 
the  incoherent  mud,  so  recently  deposited,  would  quickly  sweep  it 
out  to  sea.  Thus  sediment  such  as  that  of  the  Kimeridge  Clay  may 
have  halted  at  least  once  on  its  outward  journey.  On  the  whole, 
however,  a  continuous  movement  in  one  direction  seems  the  more 
probable,  though  it  need  not  have  been  equally  rapid  in  every  part 
.of  the  area  affected. 

Deposits  of  Jurassic  age  occur  in  Scotland,  both  on  the  shores  of 
the  Moray  Firth  and  in  the  islands  of  the  western  coast,  such  as 
Skye  and  Mull.  On  the  east  they  afford  a  fairly  continuous  section 
into  the  Upper  Oolite,  but  on  the  west  the  record  ends  with  the 
Oxford  Clay.  These  deposits  indicate  the  same  fluctuations  of  ter- 


382  THE    STORY  OF  OUR  PLANET. 

restrial,  estuarine,  and  marine  conditions  as  are  shown  in  the  Lower 
Oolites  of  Yorkshire,  and  they  were  obviously  formed  in  the  vicinity 
of  an  irregular  island-studded  coast  very  like  that  of  Western  Scot- 
land at  the  present  day.  Now  that  is  washed  by  the  Atlantic  Ocean, 
but  this  hardly  can  have  been  the  case  at  so  early  a  period  as  that 
of  which  mention  has  been  made.  Only  a  land  of  almost  conti- 
nental extent  could  have  supplied  such  great  masses  of  sediment  as 
are  embedded  in  the  Jurassic  system.  This  land  must  have  been 
larger  than  Scandinavia,  and  hardly  can  have  been  less  hilly.  The 
channel  in  which  the  Keuper  Lake  was  lodged,  as  already  said,  was 
prolonged  for  a  considerable  distance  northward,  and,  as  the  land 
sank,  it  would  be  overflowed  by  the  sea.  It  would  then  form  an 
estuary,  the  head  of  which,  no  doubt,  would  be  a  considerable  dis- 
tance from  the  open  ocean.  It  is  possible,  however,  that  the  other 
valley  which  must  have  joined  the  eastern  arm  of  the  Keuper  Lake 
may  have  been  accessible  somewhere  by  a  low  pass,  which  at  times 
may  have  been  submerged,  so  as  to  allow  of  a  complete  marine  cir- 
culation, as  there  is  through  the  Lofoten  Islands  on  the  coast  of 
Norway. 

The  Neocomian  follows  the  Jurassic  system.  On  the  continent 
of  Europe,  as  in  the  region  of  the  Swiss  Jura,  it  attains  a  great 
thickness — perhaps  as  much  as  9000  feet  of  rock — and  is  sub- 
divided into  four  groups,  each  of  which  has  received  a  name.  In 
England,  however,  the  deposits  of  this  age  do  not  cover  a  very 
large  area,  and  are  often  comparatively  thin,  although  they  are 
generally  full  of  interest.  The  succession  is  complete  in  Yorkshire 
and  in  the  southeastern  districts.  In  the  former  a  few  hundred 
feet  of  clay  which  resembles  in  color  and  is  apparently  continuous 
with  the  underlying  Jurassic  Clay  represent  the  whole  thickness  of 
the  continental  Neocomian,  with  its  fine,  hard,  cream-colored  lime- 
stones. These  deposits  may  be  traced  at  intervals  southward  from 
Speeton  Cliffs  into  Lincolnshire,  where  they  become  sandy,  and  were 
probably  approaching  a  coast  line,  of  which  more  presently.  In  the 
southeastern  district  the  Neocomian  system  consists  of  a  lower 
and  larger  fresh  water  group  called  the  Wealden,  and  an  upper 
marine  group  called  the  Lower  Greensand,  the  last  named 
being  well  exhibited  in  the  Isle  of  Wight  and  in  various  parts  of 
Kent  and  Sussex.  The  existence  of  a  great  river  was  indicated  by 
the  estuarine  and  fresh  water  deposits  of  the  Purbeck ;  this,  in  the 
Weald,  had  evidently  taken  possession  of  a  larger  area  in  the  south- 
east of  Britain.  Deposits  of  fresh  water  origin  can  be  traced  from 


THE  BUILDING   OF   THE   BRITISH  ISLES.  383 

the  Dorset  coast  to  the  neighborhood  of  Boulogne,  a  distance  of  320 
miles  from  east  to  west.  The  breadth  of  the  delta,  which  was 
probably  more  or  less  triangular  in  outline,  with  its  apex  pointing 
westward,  is  less  easily  ascertained,  but  the  deep  borings  already 
mentioned  prove  that  it  did  not  reach  the  present  valley  of  the 
Thames.  It  cannot,  however,  have  extended  less  than  50  or  60 
miles.  In  parts  of  Sussex  these  fresh-water  deposits  attain  a  thick- 
ness of  nearly  2000  feet,  and  at  Swanage,  in  Dorsetshire,  are 
estimated  at  1800  feet;  but  they  thin  rapidly  to  the  west,  and  have 
not  been  found  beyond  Ridgway.  In  the  lower  half  sands  pre- 
dominate ;  the  upper  consists  of  clays,  with  thin  bands  of  fresh- 
water limestone.  If  it  had  been  possible  to  have  stood  on  the 
southern  edge  of  the  upland  which  lies  buried  beneath  the  feet  of 
Londoners,  in  the  days  when  the  sea  had  but  recently  yielded  place 
to  the  river,  we  should  have  overlooked  a  vast  marshy  plain  lying 
some  two  thousand  feet  beneath,  and  stretching  southward  as  far  as 
the  eye  could  see.  Dense  forests,  reedy  jungles,  quiet  pools,  in 
varied  iteration,  no  doubt  saved  the  vast  fen  from  absolute  monot- 
ony, and  here  and  there  the  broad  reaches  of  the  river  gleamed  in 
the  sunshine  as  it  wound  its  way  seaward  from  the  western  uplands  ; 
parted  probably  into  diverse  channels,  and  sometimes  after  heavy 
rains  overflowing  its  banks  and  making  the  whole  valley  into  one 
great  lake. 

All  this  time,  as  is  the  wont  of  deltas,  the  land  must  have  been 
sinking,  while  the  river  struggled  to  build  out  the  sea;  but  finally 
the  victory  remained  with  the  latter,  and  it  once  more  occupied  the 
southeast  of  England.  The  Lower  Greensand  group  is  about  800 
feet  thick  in  the  Isle  of  Wight,  and  half  that  amount  in  Kent.  As 
the  name  implies,  its  beds  are  generally  sandy,  and  the  uppermost 
subdivision  is  a  fawn-colored  sand,  often  very  ferruginous.  This 
may  be  traced  diagonally  across  England,  from  Dorsetshire  into 
Lincolnshire,  and  in  the  Central  Midland  and  the  East  Anglian  dis- 
tricts it  rests  upon  an  eroded  surface  of  the  older  Jurassic  rocks. 
But  it  is  generally  missing  beneath  the  London  area ;  so  that  the 
upland  already  mentioned  must  have  managed  just  to  keep  its  head 
above  water,  even  at  the  end  of  the  epoch,  although  it  cannot  then 
have  been  more  than  a  low  island,  and  these  sands  were  no  doubt 
deposited  in  a  rather  shallow  channel  with  fairly  strong  currents, 
which  at  last  connected  the  Yorkshire  sea  with  that  covering  south- 
eastern England. 

The  lower  part  of  the  Cretaceous  system  proves  to  be  inconstant 


384  THE   STORY   OF   OUR   PLANET. 

in  character  as  it  is  followed  across  England  from  south  to  north  ; 
but  the  upper,  and  far  the  larger,  portion  is  generally  very  uniform. 
At  the  base,  in  the  southeastern  districts,  a  clay  is  found,  called  the 
Gault,  which  is  followed  by  a  calcareous,  more  or  less  sandy,  deposit, 
usually  containing  numerous  glauconitic  grains  (Upper  Greensand), 
which  passes  up  into  the  thick  mass  of  soft  white  limestone  known 
as  the  Chalk.  The  first  and  second  vary  in  thickness,  but  together 
often  amount  to  from  1  50  to  250  feet  ;  the  Chalk  sometimes  attained, 
in  the  more  eastern  parts  of  England,  to  a  thickness  of  over  1000 
feet.  It  is  rather  marly  in  the  lower  part,  but  after  a  time  it 
becomes  a  very  pure  limestone,  consisting,  as  already  stated,  almost 
wholly  of  organisms  and  their  debris*  Bands  of  flint  are  frequent, 
and  these  usually  occur  in  the  upper  half. 

As  the  Gault  and  Upper  Greensand  are  followed  toward  Bedford- 
shire, the  latter  rock  disappears  and  the  top  of  the  former  begins  to 
show  signs  of  denudation.  In  the  Cambridgeshire  district  the  upper 
part  of  the  Gault  has  been  washed  away,  and  the  base  of  the  marly 
chalk  is  formed  by  a  seam  containing  green  grains  and  phosphatic 
nodules  or  fossils,  many  of  which  indubitably  have  been  derived 
from  the  Gault.  But  in  Norfolk,  as  we  may  see  in  the  cliff  at  Hun- 
stanton,  the  brown  ferruginous  sands  belonging  to  the  uppermost 
part  of  the  Neocomian  system  are  covered  by  a  bed  of  chalk  bkiod- 
red  in  color.  This  is  only  about  four  feet  thick,  and  it  is  followed 
by  the  usual  slightly  marly  white  chalk.  Here,  then,  this  thin 
seam  occupies  the  interval  which  usually  is  filled  by  the  whole  of  the 
Gault  and  the  Upper  Greensand  together.  It  may  be  followed 
through  Lincolnshire  into  Yorkshire,  thickening  slightly  as  it  goes, 
until  when  it  comes  to  the  sea  at  Speeton  Cliff  it  has  reached  about 
30  feet. 

The  Gault,  as  it  is  followed  westward  into  Dorsetshire,  loses  its 
clayey  character  and  resembles  that  of  the  Upper  Greensand  ;  so 
that  it  can  only  be  identified  by  its  fossils  —  as,  for  instance,  is  the 
case  at  Blackdown,  in  Somersetshire.  In  the  west  of  England  the 
Chalk  is  represented  merely  by  a  few  outlying  patches,  generally 
belonging  to  this  lower  part.  But  deposits  of  unworn  flints,  form- 
ing a  sort  of  gravel  or  breccia,  may  be  found  here  and  there  lying 
upon  the  old  Primary  or  the  crystalline  rocks  as  far  as  the  Scilly 
Isles.  They  are  the  residues  of  much  greater  rock  masses,  from 


*  The  white  chalk  often  contains  full  98  per  cent,  of  carbonate  of  lime  ;  the  gray,  or 
pure,  chalk  contains  4  or  5  per  cent,  more  of  earthy  matter.     (See  p.  4.) 


less 


THE   BUILDING   OF    THE  BRITISH  ISLES.  385 

which  the  solvent  action  of  water  has  removed  the  intervening  lime- 
stone, and  they  indicate  that  the  sea  in  which  chalk  was  deposited 
extended  far  away  to  the  west  beyond  the  last  patch  of  this  rock 
which  at  present  remains. 

The  foraminiferal  ooze  which  is  dredged  up  from  the  deeper  parts 
of  the  ocean  *  resembles  the  white  chalk  more  nearly  than  any  other 
rock.  We  must  not,  however,  too  hastily  conclude  that  the  waters 
in  any  part  of  the  Cretaceous  period  rolled  full  a  thousand  fathoms 
above  the  present  site  of  the  valley  of  the  Thames.  As  will  be  seen 
when  we  review  the  past  physical  geography  of  Europe,  the  area 
occupied  by  Chalk  is  more  restricted  than  it  should  be  if  this  rock 
had  been  formed  in  oceanic  depths.  The  fauna  also  of  the  Chalk, 
regarded  as  a  whole,  is  not  indicative  of  such  conditions.  Some  of 
its  members  might  have  lived  at  depths  hardly  exceeding  100 
fathoms;  most  of  them  are  not,  strictly  speaking,  "abyssal."  As 
Professor  Prestwich  says,f  at  the  conclusion  of  an  excellent  review 
of  the  evidence,  the  depths  of  this  sea  hardly  can  have  exceeded 
500  fathoms,  and  may  not  have  been  more  than  from  about  200  to 
300.  But  its  waters  must  have  been  unusually  clean.  Hence  the 
sinking  of  the  land  which  for  so  long  had  been  in  continuous 
process,  had  now  sufficed  to  put  an  end  to  the  supply  of  sediment 
and  to  the  results  of  terrestrial  denudation  on  a  large  scale,  which 
hitherto  have  so  constantly  asserted  themselves.  In  the  Keuper 
marl,  the  clays  of  the  Lias,  the  Oxford  and  Kimeridge  deposits, 
and  the  Weald,  we  have  indications  of  physical  conditions  resem- 
bling those  which  must  have  produced  the  thinner  deposit  of  the 
Gault — the  proofs  of  a  drift  of  fine  sediment  from  a  great  and 
not  very  distant  land.  Subsequent  denudation  has  removed  so 
much  of  the  Chalk  from  the  western  and  northwestern  parts  of 
England  that  we  are  mainly  left  to  conjecture  in  any  attempt 
to  sketch  the  physical  geography  of  this  epoch.  Outlying  patcher, 
indeed,  occur  even  as  far  away  as  Antrim  and  the  western  isles 
of  Scotland,  but  these  are  of  no  great  thickness,  and  represent,  as 
their  fossils  show,  quite  the  upper  part  of  the  white  chalk  of 
England.;}:  Probably  all  this  country,  with  much  of  Wales  and 

*Seep.  187. 

t "  Geology,"  part  ii.  ch.  xx. 

\  In  Antrim  they  are  underlain  by  greensands,  which  seem  to  correspond  with  the  Upper 
Greensand  and  some  of  the  marly  chalk  of  England,  so  that  apparently  a  great  gap  exists 
in  the  record.  In  Scotland  the  beds  directly  below  the  Chalk  indicate  estuarine,  perhaps 
almost  fresh  water,  conditions. 


386  THE   STORY  OF  OUR  PLANET. 

Ireland,  was  wholly,  or  almost  wholly,  submerged.  The  great  west- 
ern land  must  have  been  broken  up — probably  for  the  first  time — 
into  scattered  groups  of  islands,  pierced  by  long  fjords,  and  commu- 
nications have  been  opened  out  between  the  Atlantic  waters  and  the 
European  sea.  This  was  a  most  important  epoch  in  the  physical 
history  of  the  British  Isles;  for  by  the  time  that  it  closed  the 
western  frontier  of  the  old  ocean  barrier  must  have  been  pro- 
foundly modified,  and  all  the  lowland  region  was  covered  with  a 
thick  slab  of  white  ooze,  spread  out  like  plaster  from  a  mason's 
trowel. 

Centuries  on  centuries  must  have  passed  while  this  mass — "  thick 
and  slab  " — was  slowly  growing  ;  centuries  followed  of  which  our 
own  country  has  preserved  no  record.  Between  the  topmost  beds 
of  the  Cretaceous  system  and  the  bottommost  of  the  Tertiary  series 
in  Britain  an  enormous  interval  of  time  must  have  elapsed — an 
interval  long  enough  to  make  a  complete  change  in  the  fauna,  for 
hardly  a  single  species  has  crossed  the  gulf  between  the  older  and 
the  newer  epochs.  A  fuller  account  of  this  change — perhaps  in 
some  respects  the  most  remarkable  in  the  geological  record — must 
be  left  for  another  chapter ;  this  must  be  restricted  to  the  physical 
geography.  Throughout  the  greater  part  of  the  Tertiary  era  the 
western  and  northwestern  part  of  Britain  appears  to  have  been  dry 
land.  The  Eocene  and  Oligocene  deposits  (for  it  is  needless  to 
separate  them  in  a  general  description)  attain  a  maximum  thickness 
of  some  2000  feet,  and  are  variable  in  character.  The  chief  sub- 
divisions can  best  be  noticed  in  passing.  When  first  the  record 
becomes  legible,  we  see  that  a  triangular  area  on  either  side  of  the 
present  Thames  was  occupied  by  a  shallow  sea  which  extended  east- 
ward toward  Northern  France  and  Belgium.  In  this  was  deposited 
the  light-colored  quartz-sand  called  the  Thanet  Sand,  a  mass  seldom 
so  much  as  60  feet  in  thickness.  A  study  of  the  area  occupied  by  this 
stratum  leads  to  the  conclusion  that  in  the  general  elevation  which 
closed  the  Cretaceous  period  the  ground  had  risen  in  the  region  of 
the  Weald  of  Kent  and  Sussex,  and  the  surface  here  was  a  few  hun- 
dred feet  higher  than  it  was  further  north.  In  the  one  place  a  low 
dome-like  mound  had  formed,  in  the  other  a  shallow  trough.  The 
axis  of  the  elevation  extended  from  west  to  east,  indicative  of  a 
feature  on  the  earth's  crust  which  afterward  assumes  a  greater 
importance.  But  after  this  crumple  was  formed  the  whole  region 
east  of  a  line  extending  roughly  from  the  Wash  to  Torbay  gradu- 
ally sank  down.  The  movement  at  first  must  have  been  extremely 


THE  BUILDING   OF    THE  BRITISH  ISLES.  387 

slow,  for  the  marine  deposits  of  the  Thanet  Sand  *  are  succeeded 
by  the  estuarine  and  fluviatile  beds  of  the  Woolwich  and  Reading 
group,  which  can  be  traced  as  far  south  as  the  Isle  of  Wight  and  as 
far  west  as  Wiltshire.  The  great  western  river  by  which  the  sands 
and  clays  of  the  Weald  were  deposited  again  asserts  itself,  though 
much  less  conspicuously,  for  the  total  thickness  of  this  Tertiary 
group  is  less  than  a  hundred  feet.  Then  the  sea  again  rolled  in  as 
the  land  sank  more  rapidly.  A  shingle  bed  in  the  "metropolitan 
area  marks  its  advance,  and  forms  a  basement  to  the  so-called  Lon- 
don Clay.  This  stiff  tenacious  deposit  can  be  traced  from  the  valley 
of  the  Thames  northward  as  far  as  Yarmouth,  in  Norfolk,  southward 
to  the  Isle  of  Wight,  and  westward  into  Wiltshire.  It  is  often  from 
300  to  400  feet  thick ;  occasionally  it  exceeds  500  feet.  All  the 
southeast  of  England  must  have  been  submerged,  but  it  is  just 
possible  that  a  low  dome-like  island  may  have  risen  above  the  cen- 
tral part  of  the  present  valley  of  the  Weald.  The  London  Clay, 
like  those  already  described,  is  formed  by  the  mud  brought  down  by 
large  rivers  into  the  sea.  In  several  places,  especially  in  the  island 
of  Sheppey,  the  fruits  of  various  tropical  plants  and  logs  of  wood 
perforated  by  Teredines  f  are  mingled  with  marine  shells,  which  are 
sometimes  abundant.  The  great  western  stream  was  probably  the 
chief  contributor  to  this  deposit,  but  its  extension  northward  to 
Yarmouth  may  indicate  that  the  northeastern  river,  which  has  been 
already  mentioned,  resumed  its  course  after  the  submergence  in 
Cretaceous  times.  This,  however,  is  "  positively  its  last  appearance  " 
on  the  geological  stage. 

The  group  of  deposits  which  succeeds  the  London  Clay  indicates 
more  estuarine  conditions.  Sands,  on  the  whole,  dominate  over 
clays,  but  the  Bracklesham  beds  of  Sussex,  which  can  be  traced, 
though  in  a  more  arenaceous  form,  over  much  of  Hampshire  and  in 
the  Isle  of  Wight,  together  with  the  Barton  Clay — somewhat  later 
in  date — of  the  latter  district,  indicate  that  the  downward  movement 
was  at  times  more  rapid.  Plant  remains  which  occur  at  various 
horizons  on  the  western  part  of  the  area  indicate  the  inflow  of  at 
least  one  important  river  from  that  side4  Unfortunately  the 
record  soon  breaks  off  on  the  north  of  the  Thames,  only  a  few 

*  The  Thanet  Sand  can  be  traced  northward  as  far  as  Suffolk. 

f  The  Teredo  is  a  mollusk,  which  still  survives  and  makes  burrows  in  piles  and  floating 
timber. 

\  It  is  now  believed  that  the  lacustrine  deposits  of  Bovey  Tracey,  in  Devonshire,  belong 
to  the  Eocene,  probably  to  the  epoch  succeeding  the  London  Clay. 


388 


THE   STORY  OF  OUR  PLANET. 


isolated  patches  of  sand  capping  the  London  Clay,  and  indicating 
that,  for  a  time  at  least,  the  sea  extended  for  some  distance  beyond 
that  valley.  The  great  western  river  still  contributed  largely  to  the 
sediment,  but  as  by  this  time  much  of  Britain  had  become  dry  land, 
other  important  streams  in  all  probability  emptied  themselves  into 
this  Anglo-Parisian  sea,  which  never  can  have  been  at  all  deep.  It 


FIG.  137.— RESTORATION  OF  THE  GEOGRAPHY  OF  BRITAIN  IN  LONDON  CLAY 

TIMES.     {After  Jukes-Brownf.} 

Water  and  land  as  in  Fig.  133. 

may  have  presented  a  very  rough  resemblance  to  the  Adriatic,  but 
in  which  direction  it  communicated  with  the  open  ocean  cannot  be 
easily  determined. 

The  area  over  which  the  geological  record  is  preserved  continues 
to  diminish,  and  the  deposits  which  formerly  were  assigned  to  the 
later  Eocene,  but  now  to  the  earlier  part  of  the  Oligocene,  are 
almost  restricted  to  the  Isle  of  Wight.*  Here  they  are  mainly  of 

*  The  principal  subdivisions  are  the  Headon  Beds,  the  Benbridge  Beds  (wholly  fresh 
water),  and  the  Hempstead  Beds  (estuarine  and  marine). 


THE  BUILDING   OF    THE  BRITISH  ISLES.  389 

fresh-water  origin,  but  estuarine  conditions  are  indicated  in  the 
middle  of  the  Headon  Beds,  and  the  record  terminates  with  a 
marine  clay,  which  points  to  a  more  rapid  downward  movement, 
leading  to  a  recurrence  of  conditions  resembling  those  under  which 
the  Barton  Clay  was  deposited.  During  this  period,  as  will  be 
indicated  in  the  next  chapter,  great  changes  were  being  made  in 
the  physical  geography  of  Europe,  which  no  doubt  produced  their 
effects  in  Britain. 

After  this  the  record  for  a  considerable  time  is  a  blank.  There 
is  not  a  single  deposit  in  all  England  which  can  be  assigned  to  the 
Miocene  period,  as  it  is  at  present  defined.  This  was  an  age  of 
sculpturing,  not  of  building — when  the  lowland  districts  were 
carved  into  hills  and  valleys,  and  the  first  outlines  of  their  physical 
features  were  rudely  blocked  out.  But  while  the  struggle  between 
land  and  sea,  which  has  been  sketched  in  the  preceding  paragraphs, 
was  being  waged  over  .the  southeastern  half  of  England,  the 
western  side  of  the  British  Isles  witnessed  events  of  a  more  star- 
tling character.  This  region,  as  has  been  said,  shared  to  some 
extent  in  the  downward  movement  which  characterized  the  Creta- 
ceous period.  The  depression  probably  reached  its  maximum  at 
the  time  when  the  record  closed  in  England,  and  when  the  chalk  of 
Antrim  and  Mull  was  deposited.  The  movements  of  the  crust 
which  replaced  for  a  time  deposition  by  denudation,  and  produced 
the  gentle  undulation  of  the  Weald  region,*  seem  to  have  disturbed 
the  equilibrium  of  Nature  more  seriously  in  northwestern  Britain, 
and  resulted  in  a  succession  of  volcanic  outbursts,  long  in  duration 
and  terrible  in  intensity,f  over  a  broad  belt  of  country,  extending 
at  least  from  Carlingford,  in  Ireland,  to  the  extreme  north  of  Skye,  on 
the  west  coast  of  Scotland.  Eruption  succeeded  eruption,  volcanic 
mountains  were  built  up,  in  some  places  probably  as  high  as  Etna, 
and  vast  sheets  of  lava  were  ejected,  which  flowed  away  in  streams 
from  the  cones,  or  welled  up  through  fissures,  till  they  covered  some 
hundreds  of  square  miles. 

The  rocks  in  many  places  are  rent  and  riven  with  dykes.  How 
far  these  extend  to  the  eastward  is  difficult  to  determine,  but  it  is 
almost  certain  that- some  of  the  dykes,  even  in  northeastern  Eng- 
land, must  be  referred  to  this  age4  It  was  an  age  of  fire,  the  like 

*  P.  386. 

f  These  have  been  described  by  Professor  Judd  in  a  series  of  papers  published  in  the 
Quarterly  Journal  of  the  Geological  Society.  The  first  appeared  in  1874. 

\  Such  as  the  Cleveland  Dyke,  ia  Yorkshire,  which  cuts  through  rocks  ranging  from  the 


39° 


THE   STORY  OF  OUR  PLANET. 


of  which  had  not  been  seen  since  the  days  of  the  Old  Red.  Sandstone. 
It  lasted  long  enough  to  eject  huge  masses  of  lava,  ash,  and  agglom- 
erate, which  differed  greatly  in  mineral  characters,  and  before  it 
closed  sufficient  time  had  elapsed  to  furrow  the  plateaus  with  deep 
valleys,  down  which  the  molten  streams  from  the  latest  outbursts 
flowed.  The  Red  Hills  of  Skye  and  the  wild  crags  of  the  Cuchullin 
range  have  been  sculptured  out  of  the  deep-seated  masses  from 
which  the  volcanic  cones,  now  vanished,  were  supplied.  Staffa,  the 


FIG.  138.  —  SECTION  OF  THE  SCUIR  OF  EIGG  (Sir  A.  Geikie). 

(6)  Dykes  cutting  through  the  plateau  composed  of  lava  flows  and  (c)  old  river  gravel  :  (/)  pitchstone 
of  the  Scuir. 


Treshnish  Islands,  and  the  plateau  of  Antrim  are  fragments  of  the 
floods  of  basalt;  all  these  attest  not  only  the  grandeur  of  the  erup- 
tions, but  also  the  erosive  force  of  wave  and  stream.  Nowhere, 
however,  is  the  lesson  taught  more  impressively  than  in  the  island 
of  Eigg.  All  who  have  traveled  along  the  west  coast  of  Scotland 
are  familiar  with  the  Scuir,  that  mighty  wall  of  rock  which  crowns 
the  steeply  sloping  ridge  back  of  the  island.  It  is  a  rendering  in 
stone  of  the  saying,  "  Every  valley  shall  be  exalted."  Where  the 
Scuir  now  rises,  there,  after  the  most  violent  outbursts  had  ended,  a 
vast  plateau,  built  up  of  flows  of  lava  and  occasional  beds  of  volcanic 


Carboniferous  to  the  Jurassic,  and  ends  near  the  sea,  south  of  Whitby,  after  a  course  of 
90  miles,  according  to  the  most  recent  estimate. 


THE  BUILDING  OF   THE  BRITISH  ISLES.  391 

ash,  stretched  away  on  every  side.  It  attained  a  thickness  of  not 
less  than  eleven  hundred  feet  above  the  Jurassic  deposits  on  which 
it  rests.  A  long  pause  followed,  during  which  rain  and  stream 
went  on  with  their  work,  till  they  had  excavated  a  valley  at  this 
place  probably  quite  four  hundred  feet  deep.  Its  bed  was  strewn 
with  fragments,  more  or  less  water-worn,  not  only  of  basalt,  but  also 
of  older  rocks,  which  at  present  occur  miles  away  to  the  north. 
Then  a  volcano  broke  out  somewhere  on  the  flank  or  in  the  bed  of 
this  valley.  Its  lava  flows  poured  down  the  glen  till  this  was  filled 
by  a  mass  of  black  glass,  which  differs  greatly  in  chemical  composi- 
tion from  the  basalt  forming  the  walls  of  the  ravine.  That  done, 


FIG.  139. — SECTION  AT  LENHAM  (J.  Prest-wicK). 

Showing  the  present  outline  of  the  ground,  the  probable  extension,  originally,  of  the  Pliocene 
deposit  (a),  and  the  chalk,  etc.,  since  removed  by  denudation. 


denudation  again  set  in,  and  rain  and  stream,  wind  and  wave,  con- 
verted the  plateau  into  an  island,  and  the  valley  into  a  fragment, 
until  at  last  its  sides  were  wholly  carved  away,  and  the  lava  stream 
which  had  flowed  along  its  floor  was  left  perched  on  high  above 
the  slopes,  which  lead  down  to  the  sea  from  the  dry  bed,  where 
the  gravel  of  the  ancient  river  may  still  be  found.* 

Pliocene  deposits  cover  only  a  comparatively  limited  area  in 
Britain.  Of  these  a  small  patch  of  clay,  near  St.  Erth,  in  Corn- 
wall, may  prove  to  be  the  earliest  representative,  if,  indeed,  it  may 
not  claim  admission  into  the  Miocene  ;f  but  with  this  exception 
they  are  restricted  to  the  eastern  side  of  England.  The  older  and 
thicker — though  it  does  not  exceed  seventy  feet — but,  so  far  as  is 
known,  the  most  restricted  in  extent,  is  called  the  Coralline  Crag. 
This  is  generally  a  yellowish,  sandy,  calcareous  rock,  rather  friable, 

*  Some  fossil  wood  (coniferous)  has  been  found  in  the  river  gravel,  but  it  does  not  deter- 
mine the  age  very  precisely.  The  island  appears  to  have  assumed  pretty  nearly  its  present 
form  by  the  end  of  the  Pliocene  period.  I  am  indebted  to  Sir  A.  Geikie,  by  whom  the 
history  of  the  Scuir  has  been  worked  out,  and  to  the  Council  of  the  Geological  Society  for 
the  diagram  illustrating  this  description. — Quarterly  Journal,  vol.  xxvii.  1871,  p.  308. 

f  The  discovery  is  but  a  few  years  old,  and  the  examination  of  the  fossils  has  not  yet 
been  completed. 


392  THE   STORY  OF  OUR  PLANET. 

which  was  probably  deposited  in  a  sea  rather  less  than  a  hundred 
fathoms  in  depth.  But,  as  a  marked  unconformity  separates  it  from 
the  overlying  Red  Crag,  a  considerable  thickness  may  have  been 
removed.  The  Red  Crag  is  usually  a  ferruginous  sand  or  gravel ; 
it  indicates  a  shallower  sea,  and  more  variable  conditions  of  deposit, 
but  it  covers  a  much  larger  area  than  the  other.  At  Lenham,  on 
the  North  Downs,  some  pipes  in  the  chalk  contain  sandy  gravel 
which  resembles  the  Red  Crag  in  color,  but  the  fossil  evidence 
justifies  the  reference  of  it  to  the  earlier  period,  when  the  depres- 
sion of  the  land,  as  already  said,  was  greater. 

The  Red  Crag  is  succeeded  by  some  clayey,  sandy,  and  gravelly 
deposits,  which  in  one  case  may  represent  a  portion  of  it.*  These 
practically  bring  the  Pliocene  period  to  a  close,  and  indicate  the 
approach  of  the  marked  climatal  changes  which  ushered  in  the 
Pleistocene  or  post-Tertiary  epoch.  One  of  them  suggests  the  con- 
clusion that,  when  it  was  deposited,  part  of  the  bed  of  the  North 
Sea  had  become  dry  land,  and  that  a  large  river,  possibly  formed 
by  the  junction  of  the  Rhine  and  the  Thames,  passed  along  the 
Norfolk  coast,  very  near  to  the  site  of  Cromer.  We  see,  then,  that 
in  the  course  of  the  Miocene  and  Pliocene  periods  the  direction  of 
the  drainage  from  the  eastern  side  of  England  and  the  opposite 
parts  of  Europe  was  changed,  so  that  the  flow  of  water  and  the 
transference  of  sediment  was  no  longer  from  north  to  south,  but  in 
the  contrary  direction.  By  the  close  of  the  Pliocene  period  the 
present  physical  geography  of  the  British  lowlands  must  have  been 
sketched  out,  and  the  rivers  must  have  occupied  valleys  which  cor- 
responded, on  the  whole,  with  those  along  which  they  are  still 
flowing.  Since  then  changes  far  from  unimportant  have  occurred. 
Channels  have  been  deepened,  widened,  in  a  few  cases  deserted  and 
a  new  path  adopted  ;  but  a  map  of  England  at  the  Cromer  Forest 
Bed  epoch,  if  drawn  on  a  small  scale,  probably  would  not  have  dif- 
fered very  materially  from  one  of  the  present  day,  except  in  the 
position  of  the  coast  line. 

Bearing  this  fact  in  mind,  we  will  endeavor  to  indicate  as  briefly 
as  possible  the  main  facts  of  the  final  chapter  in  the  physical  history 
of  the  British  Islands.  The  subject  is  full  of  difficulties,  and  has 
borne  an  abundant  crop  of  controversial  writings.  All  geologists, 
however,  are  thus  far  in  agreement :  That  during  the  later  part  of 

*  There  are  many  difficulties  as  to  the  precise  correlation  of  these  deposits,  the  united 
thickness  of  which  does  not  exceed  a  few  yards  ;  but  on  these  we  must  not  dwell. 


THE  BUILDING  OF   THE  BRITISH  ISLES.  393 

the  Pliocene  period  there  was  a  marked,  perhaps  a  rather  rapid,  fall 
of  temperature,*  not  only  in  these  islands,  but  also  in  a  large  part, 
if  not  the  whole,  of  the  northern  hemisphere.f  The  more  moun- 
tainous districts  of  Scotland,  Ireland,  Wales,  and  England  were 
covered  with  snow  and  glaciers  ;  deposits  are  spread  over  a  large 
part  of  the  lowlands,  which  sometimes  attain  a  thickness  of  from 
100  to  quite  200  feet,  and  are,  directly  or  indirectly,  the  product  of 
ice.  These  deposits  consist  partly  of  sand  or  gravel,  partly,  and 
more  characteristically,  of  bowlder  clay.  This  material  is  generally 
a  stiff  tenacious  clay,  the  nature  and  color  of  which  is  rather  varia- 
ble, for  at  least  a  part  of  its  materials  has  evidently  been  derived 
from  older  argillaceous  strata,  which  come  to  the  surface  at  no 
great  distance.  It  contains  many  fragments  of  harder  rocks,  both 
rounded  and  angular,  limestones  of  various  sorts,  chalk — pebbles  of 
this  being  very  common — flint,  shales,  including  even  such  a  perish- 
able deposit  as  the  Kimeridge  clay,  sandstones,  and  grits  ;  contribu- 
tions, in  short,  from  all  kinds  of  Secondary  and  Primary  rocks,  with 
fragments  of  various  crystalline  rocks,  such  as  granite,  basalt,  and 
schists.  These  last  have  come  from  Scotland,  or  possibly,  in  some 
cases,  even  from  Norway.  In  a  word,  clay  and  fragments  alike 
commonly  testify  to  a  drift  of  material  in  a  direction  roughly  south- 
ward. Occasionally  these  fragments  reach  a  huge  size.  On  the 
coast  of  Norfolk,  on  either  side  of  Cromer,  masses  of  rock,  measur- 
ing from  fifteen  to  twenty  yards  in  length,  are  fairly  common,  and 
they  sometimes  attain  a  much  greater  length,  though,  as  a  rule, 
they  are  not  more  than  four  or  five  yards  thick.  Most  of  these  are 
chalk,  and  this  apparently  the  chalk  of  the  adjacent  regions ;  some, 
however,  are  gravel.  These  must  have  been  frozen  solid  in  order  to 
travel.  At  Roslyn  Hill  pit,  near  Ely,  a  mass  of  chalk  has  been 
quarried  away  which  was  embedded  in  bowlder  clay,  and  must  have 
been  full  400  yards  in  length.  Both  on  the  eastern  and  the 
western  sides  of  England  there  appear  to  be  an  upper  and  a  lower 
mass  of  bowlder  clay,  with  more  gravelly  beds  between,  but  the 
latest  of  these  deposits  is  much  more  widely  distributed  than  the 
earliest,  which  is  commonly  limited  to  the  eastern  and  western 
coasts.  This  tripartite  arrangement  is  by  no  means  constant.  We 
may,  however,  affirm  that  if  in  the  inland  districts  only  a  clay 

*  The  explanations  offered  of  this  change  of  climate  will  be  mentioned  in  a  later 
chapter. 

f  There  is  evidence  of  a  similar  epoch  of  cold  in  the  southern  hemisphere,  but,  as  yet, 
it  has  not  been  proved  that  the  two  were  simultaneous. 


394  TtiE   STORY  OF  OUR  PLANET. 

occurs,  it  belongs  to  the  upper  division  ;  and  that  when  both  this 
and  gravel  are  found  in  connection,  the  latter  is  generally  the  lower 
of  the  two. 

What,  then,  is  the  history  of  this  singular  group  of  deposits  ? 
Here  geologists  are  at  issue,  differing  chiefly  in  their  views  as  to  the 
origin  of  the  bowlder  clay.  One  party  regards  it  as  the  direct  prod- 
uct of  land  ice,  the  moraine  prof onde  of  an  ice  sheet;  the  other,  as 
composite  and  more  variable  in  origin,  and  though  due  indirectly  to 
the  action  of  ice,  as  deposited  for  the  most  part  under  water.  Thus 
the  one  maintains  that  during  the  Glacial  epoch  the  land  stood  at  a 
rather  higher  level  than  at  present,  the  other  that  it  was  generally 
lower,  and  that  the  depression  at  one  time  was  very  considerable. 
They  would  not,  however,  deny  that  when  the  temperature  was 
most  severe  Scotland  must  have  resembled  the  southern  part  of 
Greenland  ;  that  Snowdon  and  Helvellyn  were  the  centers  of  glacier 
systems  which  filled  every  valley  in  the  surrounding  mountain 
regions  and  came  down  to  the  sea  ;  that  even  the  Pennine  Hills  and 
minor  groups,  like  those  of  Charnwood  Forest,  may  have  had  their 
permanent  snowfields ;  but  these  geologists  hesitate  to  bury  almost 
all  Britain  beneath  an  ice  sheet  which  extended  as  far  south  as  the 
northern  border  of  the  valley  of  the  Thames.*  One  school  of 
modern  glacialists  has  not  shrunk  from  enveloping  the  Arctic  regions 
with  one  vast  ice  cap  which  swept  in  its  slow  and  unresisted  march 
over  these  islands,  and  from  drowning  a  large  part  of  North  Central 
Europe  in  the  waters  of  a  huge  lake,  formed  of  the  rivers  ponded 
back  by  the  margin  of  this  gigantic  ice  sheet.  That,  however,  may 
be  regarded  as  the  view  of  extremists.  A  much  larger  and  more 
moderate  school  supposes  that  the  ice  sheets  originated  in  the 
various  mountain  groups  which  extend  along  the  northwestern 
margin  of  the  continent  of  Europe — Scandinavia,  Scotland,  the  North 
of  Ireland,  the  Lake  District,  and  Wales,  each  forming  an  independ- 
ent center  of  supply,  but  contributing  to  a  common  sheet  of  ice, 
the  southern  margin  of  which  possibly  extended  as  far  south  as  the 
"northern  heights  "  of  London.  By  these  geologists  the  bowlder 
clay  is  regarded  as  a  land  deposit ;  the  intercalated  sands  and  gravels, 
as  formed  by  streams,  or  in  lakes  produced  by  the  ice  locally 

*  True  bowlder  clay  is  found  about  Finchley,  Muswell  Hill,  Hendon,  on  the  higher 
ground,  but  after  that  is  not  seen  again  till  the  coast  of  Sussex  (near  Pagham  and  Selsea), 
and  this  deposit  is  universally  admitted  to  be  quite  distinct.  The  erratics  indicate  a  drift 
from  the  west  and  south.  (See  Clement  Reid,  Quarterly  Journal  of  the  Geological  Society, 
1892,  p.  344.) 


THE  BUILDING  OF   THE  BRITISH  ISLES.  395 

obstructing  the  course  of  rivers,  and  as  indicating  a  temporary 
amelioration  of  the  severest  climate.  A  third  school,  however, 
maintains  that  during  the  Glacial  epoch  the  land,  generally,  over 
the  British  Islands,  at  first  slowly  sank  and  then  as  slowly  rose  ;  that 
its  level  at  the  outset  in  all  probability  was  somewhat  higher  than 
at  present,  but  that  afterward  there  was  a  steady  depression,  more 
marked  on  the  western  than  on  the  eastern  side  of  Britain,  since  it 
amounted  on  the  former  to  some  1300  feet,  possibly  even  to  more 
than  2000,  but  on  the  latter  to  less  than  half  this  amount.  By  these 
geologists  the  bowlder  clays  are  considered  to  have  been  deposited 
in  the  shallower  water  during  the  earlier  and  later  part  of  the  epoch, 
when  the  sea  was  full  of  floating  ice,  the  greater  portion  of  this 
being,  not  bergs  from  huge  glaciers,  but  coast  ice,  which  had  formed 
on  the  shores  of  a  sea  studded  with  islands.  According  to  this  view 
the  bowlder  clays,  which  occur  at  various  heights,  frequently  up  to 
about  400  feet  above  the  present  level  of  the  sea,*  and  occasionally 
up  to  more  than  twice  that  elevation,  represent  conditions  such  as 
now  exist  in  many  parts  of  Baffin  Bay,  while  the  sands  and  gravel 
indicate  that  the  sea  was  then  more  free  from  ice,  and  its  depth 
generally  was  greater. 

The  space  at  our  disposal  does  not  permit  of  anything  more  than 
a  mention  of  the  chief  arguments  on  which  the  controversy  turns. 
The  last-named  school  urges  the  difficulties  which  are  involved  in 
attributing  to  the  action  of  land  ice  a  deposit  like  the  bowlder  clay 
which  is  found  on  the  plateau  of  Suffolk,  sometimes  80  or  100  feet 
thick,  at  a  height  of  full  300  feet  above  the  sea,  and  in  the  valley 
of  the  Cam  certainly  not  less  thick,  with  its  base  occasionally  slightly 
below  the  present  Ordnance  datum  line.  Such  an  uphill  and  down- 
dale  movement  in  an  ice  sheet  which  must  have  originated  on  ground 
comparatively  low  seems  to  them  incredible,  and  they  point  to  the 
occurrence  of  marine  shells,  occasionally  in  the  bowlder  clay,  and 
not  unfrequently  in  the  sands  and  gravels,  as  proofs  of  a  submer- 
gence. Most  of  the  arguments  on  both  sides  are  of  a  rather  indirect 
character ;  the  last  one,  however,  is  more  direct ;  the  frequent 
occurrence  of  marine  shells  in  a  deposit  anterior  to  the  age  of  man 
is  generally  held  to  be  an  indication  that  the  locality  has  been 
under  the  sea.  It  was  the  line  of  reasoning  adopted  in  the  opening 
pages  of  this  book.  "The- onus  probandi  is  accordingly  thrown  upon 


*  This  statement  applies  more  strictly  to  the  bowlder  clays  belonging  to  the  later  part  of 
the  epoch  ;  that  representing  the  earlier — the  Till — does  not  extend  above  some  200  feet. 


390  THE   STORY  OF  OUR  PLANET. 

those  who  make  the  contrary  assertion,  and  they  meet  the  argument 
by  the  following  hypothesis :  The  ice  sheet  in  passing  over  the 
bed  of  the  Irish  Channel  or  of  the  North  Sea  is  supposed  to  have 
plowed  up  masses  of  shelly  gravel,  and  to  have  transported  them 
therefrom,  often  with  their  fragile  contents  uninjured,  to  the  spot 
on  which  they  are  now  found.  The  hypothesis  is  ingenious ;  but 
many  geologists,  including  the  present  writer,  question  almost  every 
assumption  on  which  it  is  founded,  and  are  unable  to  understand 
how  a  glacier  could  possibly  transport  shells  over  very  irregular 
ground  and  deposit  them  in  well-stratified  gravels  on  such  places  as 
Moel  Tryfan*  (which  at  that  time  ought  to  have  been  covered  by 


FIG.  140. — SECTION  OF  BURIED  RIVER  CHANNEL  IN  ESSEX  ( W.  Whitaker). 
0)  Alluvium  and  river  gravel ;  (2)  old  river  gravel ;  (3)  Glacial  drift ;  (4)  chalk. 

ice)  or  Gloppa,  near  Oswestry,  where  numerous  shells  have  been 
found  belonging  to  over  sixty  species,  many  of  them  uninjured.f 

The  ice  gradually  melted  away,  the  climate  slowly  improved. 
The  rivers,  where  the  land  had  been  buried  either  beneath  glaciers 
or  beneath  the  sea,  began  to  clear  away  the  masses  of  incoherent 
debris  by  which  in  many  places  their  paths  had  been  obstructed. 
The  present  valley  systems,  as  already  remarked,  were  mapped  out 
in  preglacial  times,  but  since  then  they  have  undergone  minor 
changes,  by  no  means  inconsiderable.  It  can  be  proved  that  many 
of  the  greater  rivers  formerly  flowed  along  channels  which  followed 
slightly  different  lines  from  their  present  courses,  and  were  at  a 
lower  level.  Even  among  the  undulating  uplands  of  Essex  the 
channel  of  an  ancient  tributary  of  the  Cam  has  been  detected,  now 


*  It  is  about  1330  feet  above  sea  level,  down  to  which  glaciers  certainly  came  in  North 
Wales.  Here,  then,  the  invasion  of  North  Sea  glaciers  would  have  been  prevented. 
Moreover,  it  is  about  five  miles  from  the  sea,  and  unless  the  ice  came  from  the  west,  or 
the  shells  were  picked  up  at  the  mouth  of  the  Menai  Straits,  it  must  also  have  crossed 
Anglesey. 

f  The  place  is  about  noo  feet  above  the  sea   and  more  than  thirty  miles  from  it. 


THE  &UILDING   OF   THE  BRITISH  ISLES.  397 

buried  beneath  bowlder  clay  ;  *  but  while  in  some  cases  the  streams 
seem  to  have  done  little  more  than  clear  away  debris  and  "  return 
to  ancient  ways,"  in  others  there  is  evidence  of  no  inconsiderable 
amount  of  erosion.  Patched  about  at  various  elevations  in  the 
more  lowland  regions  are  beds  of  gravel,  often  rather  coarse,  and 
generally  indicative  of  the  action  of  streams  larger  and  stronger 
than  the  present  rivers.  When  glaciers  still  lingered  in  the  moun- 
tain valleys,  and  the  upland  districts  in  winter  time  were  swathed 
in  snow,  the  rivers  would  run  for  part  of  the  year  as  strongly  as 


FIG.  141. — SECTION  OF  THAMES  VALLEY  AT  GORING  (J.  Prestwicfi). 

(i)  Postglacial  drift  ;  (2)  Glacial  drift  ;  (3)  preglacial  gravel  ;  (4)  Lower  Tertiary  strata  ;  (5)  chalk. 

A.  Denudation  during  the  early  Glacial  period,  about   160  feet. 

B.  Denudation  during  the  later  Glacial  period,  about  220  feet. 
c.  Denudation  during  the  postglacial  period,  about  70  feet. 

they  now  do  only  in  very  exceptional  floods.  Some  of  these 
gravels  on  the  higher  plateaus  may  be  preglacial ;  some  also  which 
lie  to  the  south  of  the  Thames  may  be  contemporary  with  the 
bowlder  clay  to  the  north  of  that  river  ;  but  others,  like  the  "  plateau 
gravels  "  of  East  Anglia,  are  certainly  postglacial.  The  highest  of 
these  seem  to  have  little  connection  with  the  existing  river  systems — 
indeed,  they  may  be  a  marine  deposit — but  as  they  occur  nearer  and 
nearer  to  the  present  sea  level  they  become  more  and  more  closely 
connected  with  the  streams.  The  valley  of  the  Medway,  as  already 
mentioned, f  has  been  deepened  by  250  feet  in  postglacial  times,  that 
of  the  Thames  at  Goring,  according  to  Professor  Prestwich,  during 
the  later  glacial  and  postglacial  epoch,  by  about  290  feet ;  ^  and 
evidence  exists  in  many  places  that  rivers  have  added,  in  times 

*  The  bottom  is  rather  below  the  Ordnance  datum  line,  and  the  drift  by  which  it  is 
filled  is  in  places  218  feet  deep. — W.  Whitaker,  Quarterly  Journal  of  the  Geological 
Society,  xlvi.  p.  337.  The  diagram  on  p.  396  is  from  this  paper. 

f  See  p.  115.  The  breadth  of  the  valley  at  this  part  is  seven  miles. — Quarterly  Journal 
of  the  Geological  Society,  xxxi.  p.  465. 

\  The  amount  of  change  in  the  valley  of  the  Lower  Thames  is  a  matter  of  some  dispute, 
but  as  bowlder  clay  overlies  gravel  at  Totteridge,  and  the  same  gravel  can  be  traced  by 
Finchley  to  Hendon,  where  it  is  rather  less  than  250  feet  above  Ordnance  datum,  there 
must  have  been  a  difference  of  level  in  preglacial  times  of  nearly  200  feet,  and  the  valley 
of  the  Brent  and  of  the  Thames  must  have  been  at  least  sketched  out. 


'39^  THE   STORY  OF  OUR  PLANET. 

certainly  postglacial,  not  much  less  than  100  feet  to  the  depth  of 
their  valleys. 

Even  the  last  pages  of  the  story  of  our  planet  indicate  that 
whether  or  not  a  great  submergence  affected  these  islands  during 
the  Glacial  epoch,*  movements,  both  upward  and  downward,  have 
subsequently  occurred.  These  may  be  noticed  in  passing,  as  we 
sketch,  in  as  few  words  as  possible,  the  last  stages  of  the  develop- 
ment of  the  British'  Isles. 

The  bolder  hill  regions,  of  which  remnants  can  still  be  found,  as 
already  said,  were  all  in  existence  when  the  Secondary  era  began. 
Hence  the  excavation  of  their  valley  systems  must  have  commenced 
long  before  it  came  to  an  end.  Great  changes,  no  doubt,  were 
made  during  Tertiary  times,  but  to  escape  from  a  groove  is  no  easy 
matter  ;  hence,  unless  a  submergence  had  been  very  prolonged,  and 
the  deposit  of  material  very  great,  a  river,  when  the  land  was  once 
more  elevated,  would  almost  certainly  return  to  its  former  channel. 
Thus  these  ancient  valleys  would  produce  an  effect  upon  the  low- 
lands by  determining  the  points  where  the  chief  sculpturing  tools 
were  applied,  so  that  as  the  ground  continued  to  rise  the  highland 
valleys  would  be  prolonged  seaward  through  the  newly  exposed 
sediment.  Since  the  sea  during  Eocene  times  appears  to  have  ex- 
tended over  at  least  the  southeastern  half  of  England,  it  might  have 
been  expected  that  the  rivers  would  have  flowed  in  that  direction, 
so  as  to  discharge  the  drainage  of  the  greater  part  of  England  into 
the  sea  north  or  south  of  the  Straits  of  Dover.  But,  as  a  glance  at 
a  map  shows,  the  courses  of  the  four  most  important  rivers  are  by 
no  means  so  simple.  The  Thames,  indeed,  takes  the  direction  which 
might  have  been  expected,  but  it  rises  in  Gloucestershire,  not  in 
Wales,  and  is  altogether  a  lowland  river.  The  Dee  and  the  Severn 
rise  far  back  in  Wales,  and  when  they  issue  from  the  hill  region — 
not  very  far  apart — the  one  turns  northward  toward  the  Irish  Sea, 
the  other  southward  toward  the  Bristol  Channel,  and  the  course  of 
each  is  almost  a  semicircle.  The  comparatively  low  central  plateau 
to  the  northeast  of  Edgehill,  in  Warwickshire,  parts  the  drainage  of 
the  Wash  and  the  Thames,  and  separates  both  from  that  of  the 
Severn,  thus  occupying  a  most  important  position  in  the  physical 
geography  of  England.  Again,  a  line  running  irregularly  from  east 

*A  considerable  depression,  amounting  to  perhaps  500  feet,  would  be  admitted  for 
Britain  by  all  but  a  few  very  "ardent  glacialists."  It  seems  impossible  to  deny  that  the 
submergence  at  Montreal,  in  Canada,  amounted  to  at  least  520  feet,  and  there  is  evidence 
elsewhere,  as  already  stated,  of  a  yet  greater  depression. 


THE  BUILDING   OF    THE  BRITISH  ISLES. 


399 


to  west  through  the  southern  counties  forms  a  watershed  right  away 
from  the  Straits  of  Dover  to  Devonshire.  The  parting  of  the 
Thames  and  the  Wash  drainage  in  the  east-central  districts  pos- 
sibly may  be  related  to  the  same  feature.  How,  then,  are  these 


FIG.  142. — MAP  ILLUSTRATING  HOW  A  RISE  OF  600  FEET  (100  FATHOMS)  WOULD 
UNITE  GREAT  BRITAIN  WITH  IRELAND  AND  THE  BRITISH  ISLANDS  WITH 
THE  CONTINENT. 


anomalies  to  be  explained  ?  In  connection  with  this  a  further  ques- 
tion may  be  asked — What  account  can  be  given  of  the  Bristol  and 
St.  George's  channels  ? — for  they  bear  a  very  close  resemblance  to 
submerged  river  valleys.  This  is  the  change  which  an  elevation  of 
600  feet  would  work  in  the  latter :  The  water  would  retreat,  and 
Ireland  in  reality  fcrm  part  of  the  United  Kingdom.  A  broad  pla- 
teau, generally  300  to  400  feet  above  sea  level,  would  link  Donegal 


400  THE    STORY  OF  OUR  PLANET. 

with  Islay,  Mull,  and  the  Scotch  mainland.  This  would  slope  down, 
quickly  on  the  southern  side,  to  a  rather  wide  valley,  extend- 
ing between  Ireland  on  one  side  and  England  and  Wales  on  the 
other.  The  floor  of  this  (assuming  the  present  level  unchanged) 
would  descend  but  slightly  till  it  had  come  a  little  south  of  Cardigan 
Bay,  when  it  would  fall  below  the  3OO-foot  contour  line,  and  then 
shelve  slowly  seaward.  It  is  difficult  to  understand  how  such  a 
valley  could  be  primarily  formed  except  by  the  action  of  rain  and 
rivers,  though  in  such  case  we  must  assume  its  slope  once  to  have 
been  more  rapid  than  it  is  at  present,  for  this,  on  the  average,  is 
less  than  three  inches  to  a  mile,  and  so  is  more  favorable  to  deposi- 
tion than  to  denudation.  Irregularities  also  exist  in  the  floor,  which 
must  be  due  either  to  an  irregular  deposition  of  materials  on  it  or 
to  unequal  movements  in  it,  and  the  latter  supposition  appears  to  be 
the  more  probable.  As  the  "  valley  of  the  Irish  Sea  "  is  on  a  far 
larger  scale  than  that  of  the  Dee,  or  even  of  the  Severn,  it  may  have 
been  begun  at  a  somewhat  earlier  date,  as  in  Eocene  times,  while 
the  sea  still  covered  the  greater  part  of  England,  and  the  drainage 
of  Eastern  Wales  meandered  slowly  toward  it  over  a  strip  of 
lowland. 

Two  causes  may  have  co-operated  in  producing  this  anomalous 
direction  of  our  river  systems,  and  in  preventing  the  restoration  of 
the  western  continental  land,  after  the  Cretaceous  or  even  the 
Eocene  submergence.  The  first :  That,  as  already  mentioned,  the 
western  border  of  Britain  was  the  scene  of  great  volcanic  eruptions, 
which  began  soon  after  the  Cretaceous  period  and  continued  prob- 
ably into  the  Miocene.  These,  as  already  explained,*  might  prevent 
any  upward  movement,  and  even  produce  subsidence.  The  second 
cause  is  this :  Shortly  before  Eocene  times  the  elevation  of  a  con- 
siderable tract  of  land,  on  the  site  of  the  present  Weald  of  Kent 
and  Sussex,  had  begun,  and  movement  in  an  upward  direction 
doubtless  continued  over  an  elongated  area,  at  least  300  miles 
in  length,  until  comparatively  late  in  the  Tertiary  era.  The  system 
of  flexures,  of  which  this  formed  a  part,  very  possibly  affected,  dur- 
ing post-Eocene  times,  a  large  portion  of  the  eastern  half  of  Eng- 
land ;  so  that  on  its  western  side  the  land  was  made  to  shelve  in 
that  direction,  and  the  Sevein  and  the  Dee  were  forced  to  flow 
parallel  with  the  borders  of  Wales  until,  after  rounding  the  hill 
region,  they  ran  down  the  lowland  slopes  in  a  western  direction. 

*  P.  247. 


THE  BUILDING  OF    THE   BRITISH  ISLES.  4° I 

The  Trent,  as  its  sources  lay  further  north,  may  have  just  succeeded 
in  turning  the  southern  extremity  of  the  Pennine  Hills,  and  may 
have  been  forced  afterward  into  a  northern  course  by  the  effects  of 
some  minor  flexure.  It  has  been  suggested  *  that  this  river  origi- 
nally passed  out  seaward  through  the  gorge  in  the  Lincolnshire 
Wolds  which  is  now  occupied  by  the  Witham,  and  that  the  separa- 
tion of  the  two  rivers  and  the  diversion  of  the  former  into  the 
H  umber  may  be  an  event  later  than  the  Glacial  epoch. 

Whatever  may  have  been  the  conditions  under  which  the  bowlder 
clays  were  formed,  it  is  almost  certain  that  during  the  deepening  of 
the  river  channels,  and  the  formation  of  the  coarse  gravel  beds  men- 
tioned above,  the  land  stood  at  a  level  higher  than  at  present.  Ire- 
land, for  a  time  at  least,  was  linked  to  Scotland  ;  England,  for  long, 
was  united  to  France.  The  latter  effect  would  be  secured  by  a 
rise  of  150  feet.  Double  that  amount  would  much  more  than 
suffice  for  the  former.  But  the  area  of  England  would  be  consider- 
ably enlarged  even  by  the  smaller  elevation,  for  it  would  convert 
into  dry  land  much  of  the  Bristol  and  St.  George's  channels  and  of 
the  North  and  Irish  seas.  For  instance,  it  is  almost  certain  that  at 
this  time  a  continuous  ridge  of  chalk  extended  from  the  north  of 
Swanage  right  across  to  the  Isle  of  Wight,  from  which  ridge  a 
river  flowed  eastward  along  the  valley  of  the  Solent.  From  this  it 
follows  that  the  coast  line  of  Britain  has  been  deeply  indented  and 
sculptured,  largely  by  the  sea,  even  in  this  last  geological  epoch. 
Where  the  rocks  are  hard,  as  on  the  western  side,  there  probably  the 
work  has  been  in  process  at  least  since  the  period  of  the  Cretaceous 
submergence;  but  the  shaping  of  the  Isle  of  Wight  and  the  sever- 
ance of  England  and  France  must  be  events,  geologically  speaking, 
very  recent. 

In  many  places  round  our  coasts,  but  more  especially  on  the 
south  and  west,  the  remains  of  trees,  still  rooted  in  the  earth,  can 
be  detected  for  some  distance  below  the  level  of  high  water.  They 
are  proofs  of  a  subsidence,f  but  this  may  not  have  been  great,  for 
the  utmost  change  need  not  have  exceeded  50  feet.  Another 
group  of  facts,  however,  points  in  the  contrary  direction.  In  many 
places  on  the  coast  of  the  British  Isles  raised  beaches,  as  already 

*  By  A.  J.  Jukes-Browne,  Quarterly  Journal  of  the  Geological  Society,  xxxix.  p.  606. 

•{•  Some  geologists  are  of  opinion  that  these  submarine  forests  may  be  explained  by  the 
removal  of  underlying  sandy  beds  through  the  action  of  springs  ;  but  the  present  writer 
thinks  that,  though  this  may  have  produced  some  local  effect,  the  explanation  is  insuffi- 
cient to  account  for  all  the  phenomena. 


402 


THE   STOA'Y  OF  OUR  PLANET. 


stated,  are  found.  They  occur  at  different  elevations,  and  must  be 
referred,  of  course,  to  different  dates ;  and  even  the  same  beach,  as 
it  is  traced  along,  does  not  maintain  a  uniform  height ;  but  the 
latest,  which  is  frequently  from  20  to  30  feet  above  sea  level,* 
indicates  an  old  depression  which  is  undoubtedly  later  in  date  than 
some,  probably  all,  of  these  forests.  On  this  point,  however,  it  is  diffi- 
cult to  arrive  at  any  very  precise  conclusion,  for  the  evidence  bearing 


FIG.  143.— THE  NORTH  DOWNS  AND  WEALD  VALLEY. 


on  it  is  conflicting  and  confused.  The  raised  beaches  as  a  whole  are 
postglacial,  and  indicate  in  the  western  parts  of  Scotland  a  former 
considerable  submergence.  They  are  found  not  seldom  up  to  a 
height  of  about  350  feet,  and  may  be  traced  still  higher,  perhaps  to 
some  noo  feet.f  These,  however,  possibly  belong  rather  to  the 
later  part  of  the  Ice  Age, when  the  glaciers  were  rapidly  dwindling; 
but  the  lower  beaches  must  be  much  newer  than  the  coarse  river 
gravels,  for  in  the  former  tools  of  polished  stone,  and  even  canoes, 
have  been  found.  These  show  that  Britain  must  have  been 
inhabited  by  races  far  more  civilized  than  those  which  abode  in  it 
immediately  after  the  Glacial  epoch.  Moreover,  the  fjords  of  Nor- 
way, the  lochs  of  Scotland  and  Ireland,  the  estuaries  of  Wales  and 
Western  England  generally,  all  indicate  submerged  valleys,  and 
prove  that  the  latest  upward  movement  has  not  entirely  compen- 
sated for  a  preceding  one  in  the  contrary  direction.  This  submer- 
gence probably  enabled  the  waves  to  replace  the  isthmus  between 
Kent  and  the  Boulonnais  by  a  straft,  and  to  trespass  rapidly  on  the 

*  It  is  sometimes  called  the  "  twenty-five-foot  beach,"  as  that  is  often  its  height, 
f  The  author  considers  the  Parallel  Roads  of  Glenroy  to  \>Q  raised  beaches. 


THE  BUILDING  OF    THE  BRITISH  ISLES.  403 

southern  and  eastern  coasts  of  this  country.  Possibly  stories  of  sub- 
merged districts,  such  as  the  "  lost  land  of  Lyonesse,"  may  be  in 
reality  vague  traditions  of  primeval  days,  before  Britain  was  an 
island  or  Rome  had  been  founded.  Certain  it  is  that,  as  already 
shown,  the  process  of  change  has  continued  into  historic  times. 

When  the  history  of  the  "  building  of  the  British  Isles  "  begins, 
their  site  appears  to  be  on  the  border  of  land  and  of  sea — the  one, 
stretching  far  away  to  the  west,  part  of  a  semi-continental  mass 
which  extended  at  least  from  the  seventieth  to  the  forty-seventh 
parallel ;  the  other,  part  of  a  very  large  island-studded  sea  which 
covered  much  of  Western  and  Central  Europe.  The  history  ends  as 
an  island  group,  built  up  of  geological  fragments  of  almost  every 
age,  with  a  great  ocean  deepening  to  the  west  and  a  large  continent 
for  its  immediate  neighbor  on  the  east. 

The  hills  are  shadows,  and  they  flow 
From  form  to  form,  and  nothing  stands. 


CHAPTER  V. 

THE   BUILDING  OF   EUROPE   AND   OTHER   CONTINENTS. 

IN  the  preceding  chapter  "  the  building  of  the  British  Isles  "  has 
been  traced  at  some  length.  This  has  been  done  because  not  only 
are  the  localities  likely  to  be  familiar  to  most  readers,  but  also  a 
fairly  minute  description  of  any  one  region  may  indicate  the  nature 
of  the  process  in  other  parts  of  the  globe.  But  the  latter  must  be 
noticed  much  more  briefly.  In  their  case  the  difficulties  of  the 
task  are  far  greater,  for  information  concerning  them,  except  as 
regards  Europe,  is  often  either  very  fragmentary  or  altogether  want- 
ing. Of  this  continent  we  purpose  to  give  a  succinct  description, 
especially  of  those  parts  which  are  more  closely  related  to  the 
British  Isles,  and  to  conclude  with  a  slight  sketch*  of  the  geological 
history  of  other  quarters  of  the  globe. 

In  regard  to  Europe  time  will  be  saved,  perhaps  also  our  account 
will  be  rendered  more  intelligible,  by  reversing  the  order  of  treat- 
ment followed  in  the  case  of  the  British  Isles,  and  working  from  the 
present  physiography  to  the  past  geology.  On  examining  a  map 
of  Europe,  whereon  the  contours  are  clearly  indicated,  we  observe 
that  it  exhibits  four  distinct  types  of  surface — plains,  uplands,  high- 
lands, mountain  ranges.  Three  of  these  are  represented  in  Britain, 
though  on  a  restricted  scale  as  regards  area :  the  plains,  by  the 
fenlands  on  many  of  our  river  valleys;  the  uplands,  by  the  ordinary 
undulating  regions,  such  as  the  chalk  hills  of  Wiltshire  or  the  lime- 
stone districts  of  Somersetshire  and  Gloucestershire ;  and  the  high- 
lands, by  the  northern  part  of  Scotland.  Obviously  the  classifica- 
tion is  a  rough  one,  for  a  hard  and  fast  division  is  not  possible.  But 
the  fourth  type — the  mountain  range — strictly  speaking,  is  not  repre- 
sented in  Britain.  Of  it  the  Pyrenees,  the  Alps,  and  even  the 
Apennines  and  the  ranges  east  of  the  Adriatic,  are  examples.  These 
seem  to  be  in  some  way  connected  with  the  Mediterranean  Sea  and 

*In  writing  this  sketch  I  have  made  great  use  of  Professor  Kayser's  "Text-book  of 
Comparative  Geology  "  (translated  and  edited  by  Mr.  P.  Lake),  and  consulted  with  much 
advantage  Sir  A.  Geikie's  "  Text-book  of  Geology  "  and  Professor  Prestwich's  "  Geology," 
vol.  ii.,  which  contains  an  admirable  geological  map  of  Europe, 


THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS.       405 

its  associated  basins,  while  the  highland  type  belongs  to  the  regions 
which  are  more  nearly  related  to  the  Atlantic  and  Arctic  oceans. 
On  examining  a  geological  map  we  find  the  distinction  between 
these  two  types  to  be  connected  with  a  difference  in  age.  The 
mountain  ranges  are  comparatively  modern  in  date  :  the  highland 
regions  have  existed  from  an  antiquity  much  more  remote.  In  their 
day  they  also  may  have  been  mountain  ranges ;  but  time  has  told 
upon  them,  and  they  are  now  like  the  carious  stumps  of  mountain 
teeth.*  Hence,  as  we  go  back  in  geological  history,  the  grandest 
and  most  salient  features  in  the  scenery  of  Europe  are  among  the 
first  to  disappear,  and  comparatively  inconspicuous  highland  dis- 
tricts jDrove  to  be  much  more  permanent  landmarks.  These  form 
the  "horsts"(p.  218)  round  which  several  of  the  later  geological 
formations  successively  crop  out  in  almost  concentric  zones,  while 
the  former  are  like  sharp  "  plaits  "  or  "  puckers  "  of  the  crust  which 
sometimes  suddenly  interrupt  a  surface  comparatively  level.  The 
Pyrenees,  the  Alps  with  their  southern  offshoots,  the  Carpathians, 
and  the  Caucasus  are  comparatively  modern ;  but  the  Cevennes 
with  Auvergne,  the  Vosges,  the  Black  Forest,  and  the  linked  group 
of  highland  masses  which  covers  so  much  of  Central  Germany,  as 
far  as  the  "  Wald  "  of  Bavaria  and  Bohemia,  besides  a  considerable 
part  of  the  Spanish  peninsula,  are  very  old,  and  from  time  to  time 
have  played  an  important  part  in  the  physical  history  of  Europe.f 

We  have  already  spoken  of  the  close  connection  between  England 
and  France.  The  chalk  hills  which  flank  the  valley  of  the  Somme 
recall  those  south  of  the  estuary  of  the  Thames.  The  sandstones 
near  Boulogne  have  much  in  common  with  those  on  the  coast  of 
Kent.  Differences  may  exist  here  and  there ;  but  the  relationship, 
as  will  be  seen  presently,  extends  still  further.  Belgium  and  Holland, 
with  a  little  of  the  northern  part  of  France,  and  all  the  North  Ger- 
man lowland,  are  largely  covered  by  drifts  which  are  closely  allied 
to  the  Glacial  and  postglacial  deposits  of  England.  Some  geolo- 
gists believe  that  the  Scandinavian  ice  sheets  once  trespassed  further 
south  than  Berlin ;  others  refer  the  drifts  of  this  region  to  a  more 
varied  origin,  and  regard  them  as  mainly  subaqueous.  The  same 

*  This,  in  regard  to  Scotland,  has  been  brought  out  with  great  force  in  an  article  by 
Professor  J.  Geikie  in  the  Scottish  Geographical  Magazine  (vol.  ii.  p.  145),  and  it  is  no  less 
true  of  Western  Scandinavia.  The  Ardennes  are  probably  part  of  an  old  mountain  range, 
and  some  Belgian  geologists  have  asserted  that  it  once  rose  to  a  height  of  I2,OOO  feet,  or 
even  more. 

f  Volcanic  mountains  are  not  included  in  these  remarks. 


4°6  THE   STORY  OF  OUK  PLANET. 

remark  applies  to  the  Russian  lowland,  south  and  east  of  the  Gulf 
of  Finland.  There  can  be  no  doubt,  however,  that  in  the  Glacial 
epoch  the  ice  sheet  of  Scandinavia  extended  considerably  beyond 
the  present  coast  line,  and  the  glaciers  which  radiated  from  the 
Pyrenees  and,  still  more,  from  the  Alps,  came  down  to  within  a  few 
hundred  feet  of  the  sea  level.*  Those  from  the  latter  chain  have 
left  huge  moraines  on  the  plains  of  Piedmont  and  Lombardy,  and 
the  old  glacier  of  the  Rhone  extended  to  within  a  few  miles  of 
Lyons. 

In  Pliocene  ages  a  large  part  of  Europe  was  a  level  surface,  and 
the  dominant  features  of  its  scenery  did  not  materially  differ  from 
the  present,  though,  doubtless,  peaks  and  ravines,  hills  and  valleys 
were  then  less  completely  sculptured  than  they  are  now.  The  North 
Sea  occupied  a  large  area,  covering  not  only  the  east  of  England,  but 
also  Belgium  and  the  adjacent  part  of  northern  France ;  and  in  the 
south  the  Mediterranean  Sea  extended  considerably  beyond  its 
present  limits ;  for,  on  the  northern  side,  the  lower  lands  of  Italy, 
Spain,  and  Greece  were  submerged.  Fluviatile  and  terrestrial 
deposits  of  the  same  period  also  occur  both  in  these  countries  and 
in  many  parts  of  Germany  and  Austria,  while  Western  Slavonia  con- 
tains deposits  more  distinctly  lacustrine  in  origin.  The  volcanoes  of 
Italy  and  even  the  huge  mass  of  Etna  did  not  begin  their  existence 
till  late  in  Pliocene  times. 

In  the  Miocene  period,  though  a  considerable  part  of  Europe  still 
remained  dry  land,  the  areas  covered  by  sea  were  conspicuously 
augmented.  But  toward  its  end  some  very  important  changes 
occurred  in  the  physical  geography  of  the  central  region.  Disturb- 
ances affected  the  chain  of  the  Alps,  which  produced,  as  will  be 
presently  described,  the  most  marked  effects  in  the  middle  portion 
of  the  northern  face.  The  Pyrenees  and  Carpathians  were  similarly 
affected,  though  not  to  a  like  extent.  The  English  and  North 
French  areas  were  above  water ;  but  parts  of  Belgium  and  Holland, 
with  Holstein  and  Friesland,  were  occupied  by  a  sea,  and  marine 
deposits  occur  in  the  basin  of  Mayence.  Gulfs  from  the  Atlantic 
extended  into  the  lowland  districts  of  the  Loire  and  the  Garonne, 
and  overspread  much  of  the  coast  regions  of  Spain  and  Portugal. 
"  From  the  Mediterranean,  which  still  covered  large  areas  in  the 
northwest  of  Africa,  the  Miocene  sea  extended  through  the  Rhone 
valley  to  the  level  part  of  Switzerland,  and  thence  through  Upper 

*Seep.  135. 


THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS.        407 

Swabia  and  Upper  Bavaria  to  Vienna.  An  arm  of  the  sea  stretched 
north  of  the  Carpathians  to  Moravia,  probably  even  to  Galicia, 
while  a  second  formed  the  connection  with  the  great  '  Pannonian 
basin/  which  extended  over  Hungary  and  a  part  of  Steiermark, 
Carniola,  Croatia,  and  Bosnia,  and  reached  east  beyond  the  present 
Black  and  Caspian  seas,  which  are  only  the  last  remains  of  that 
great  Miocene  ocean.  The  Alps,  like  the  Carpathians,  were  still 
islands  in  the  Mediterranean,  while  the  greater  part  of  Sicily,  Malta, 
etc. — islands  formed  chiefly  of  marine  Miocene  beds — was  at  that 
time  under  the  sea."  *  The  Mediterranean,  however,  appears  to 
have  been  already  separated  from  the  Indian  Ocean,  for  no  marine 
beds  of  Miocene  age  occur  in  Egypt,  Syria,  Asia  Minor,  Persia,  or 
Arabia.  In  Europe  deposits  of  fresh  water  origin  also  are  not  un- 
frequent,  and  they  alternate  in  the  zone  north  of  the  Alps  with  the 
marine  beds  already  mentioned.  The  volcanoes  of  the  Eifel,  the 
Rhine  district,  and  the  parts  of  Germany  east  of  the  Rhine,  in 
Bavaria,  Silesia,  and  around  Schemnitz  in  Hungary,  in  Catalonia, 
and  some  of  those  in  Auvergne,  were  in  action  during  Miocene  times. 
The  great  earth  movements  which,  as  mentioned  above,  affected 
the  newer  mountain  systems  at  the  close  of  the  Miocene  period, 
must  have  finally  determined  the  present  physical  structure  of 
Europe.  As  the  highland  regions  of  Central  France  and  Germany 
were  already  in  existence,  many  of  the  river  valleys  which  radiate 
from  them  may  have  been  already  defined  ;  but  with  a  sea  on  the 
site  of  Mayence  and  fringing  the  north  face  of  the  Alps  it  is  obvious 
that  the  greater  part  of  the  courses  of  the  Rhone,  the  Rhine,  and 
the  Danube  cannot  yet  have  been  determined,  and  the  same  is  true 
of  the  lowland  portion  of  the  Po.  Since  the  sea  must  have  inter- 
cepted all  the  affluents  of  these  rivers,  as  they  emerged  from  the 
mountain  regions,  a  date  earlier  than  the  beginning  of  the  Pliocene 
period  cannot  be  assigned  to  any  part  of  their  valleys  which  is  clear 
of  the  Alps.f 

*  "  Text-book  of  Comparative  Geology,"  p.  353. 

f  The  late  Sir  A.  Ramsay  maintained,  and  his  reasons  appear  weighty  (Quart.  Jour. 
Geol.  Soc.,  vol.  xxx.  1874,  p.  81),  that  the  Rhine,  in  taking  its  present  course  through 
Germany,  occupied  the  valley  of  a  river  which  in  Miocene  times  flowed  southward  from 
the  Hundsruck  Taunus,  this  reversal  of  the  direction  of  drainage  being  connected  with  a 
general  northward  tilt  of  that  part  of  Europe,  due  to  the  last  elevation  of  the  Alpine  region. 
The  old  valley  being,  to  a  great  extent,  filled  up  by  Miocene  deposits,  the  new  stream 
would  soon  find  a  way  out  northward,  and  gradually  excavate  the  present  gorge  between 
Bingen  and  Bonn  ;  so  this  noted  feature  in  the  scenery  of  Germany  has  been  sculptured 
since  the  beginning  of  Pliocene  times. 


4°8  THE   STORY  OF  OUR  PLANET. 

In  the  Oligocene  period  a  sea  appears  to  have  spread  itself  inland 
from  the  shores  of  the  Baltic  and  the  North  Sea  over  the  lower 
ground  of  Germany  to  Leipzig,  Cassel,  and  even  Frankfort-on-the- 
Oder,  and  westward  to  the  southeast  of  England,  over  Northern 
France  and  all  around  Paris,  even  to  beyond  the  Loire.  In  the  last 
two  districts,  however,  and  in  Belgium,  the  marine  are  mingled  with 
fresh  water  beds.  Much  of  Southern  Europe  also  was  covered  by 
sea,  in  which  the  rising  Alps  and  the  old  highland  regions  of  France 
and  Germany  probably  formed  islands,  and  the  two  areas  of  salt 
water  may  have  been  connected,  at  any  rate  at  the  time  of  deepest 
submergence,  by  a  strait  running  from  Frankfort  to  Cassel.  In 
many  places  in  the  region  which  was  generally  occupied  by  the 
southern  sea  fresh  water  deposits  are  intercalated  with  the  marine, 
especially  in  the  vicinity  of  the  Alps  ;  in  others  the  latter  are  wholly 
wanting.  Among  the  highlands  of  Auvergne,  for  instance,  was 
more  than  one  lake  *  on  the  shores  of  which  the  volcanoes  were  in 
eruption  from  this  time  till  a  comparatively  late  epoch ;  streams  of 
lava  flowed  over  the  newly  formed  fresh  water  beds,  the  latter  some- 
times reaching  a  thickness  of  1500  feet.  Similar  deposits  also  are 
found  in  Provence  and  other  parts  of  Southern  France.  The  tor- 
rential rivers,  which  were  furrowing  the  newly  risen  Alps,  discharged 
huge  masses  of  coarse  gravel  upon  the  marginal  lowland,  especially 
to  the  north  of  the  central  region,  and  in  almost  every  direction 
covered  a  considerable  area  with  finer  sandstones  and  occasional 
marls.  By  the  last  set  of  movements  these  Oligocene  gravels  were 
raised  to  a  height  of  some  6000  feet  above  the  sea,  as  may  be  seen 
in  the  cliffs  of  the  Rigi  and  the  Speer.f 

In  Eocene  times  the  Alps,  Pyrenees,  Carpathians,  and  Caucasus 
had  no  existence  as  mountain  chains ;  but  we  will  defer  the  impor- 
tant question  of  their  development  until  the  general  structure  of  the 
continent  at  this  period  has  been  noticed.  During  a  considerable 
part  of  it  much  of  Europe  was  covered  by  sea.  A  large  land  area, 
indeed,  very  probably  occupied  the  northern  region,  including  not 
a  little  of  Russia,  and  extending  thence  westward  by  Scandinavia  on 
to  Britain  ;  but  this  was  bounded  by  a  sea  on  the  south,  which 
apparently  covered  part  of  North  Germany,  Denmark,  Belgium, 

*  The  largest,  which  covered  the  site  of  Clermont  Ferrand,  was  some  twenty  miles  wide 
and  more  than  ninety  long. 

f  The  pebble  beds  go  by  the  name  of  nagelfinh  (nail  rock) ;  the  sandstones  are  called 
morasse.  The  group,  for  the  most  part,  is  of  fresh  water  origin,  and  a  lake  may  have 
extended  then  over  a  considerable  part  of  Northern  Switzerland. 


THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS.        469 

Northern  France,  and  Southeastern  England.  Beyond  this,  in  the 
same  direction,  lay  land  or  a  closely  connected  group  of  islands,  and 
then  came  a  sea  which  occupied  "  the  whole  of  South  Europe  "  and 
the  present  Mediterranean  area,  whence  it  extended  southward  far 
into  Africa,  and  eastward  right  across  Asia  to  join  the  Pacific  Ocean. 
Here  and  there,  however,  it  was  interrupted  by  islands,  now  incor- 
porated into  the  Alps,  Carpathians,  Pyrenees,  and  Apennines.  In 
this  wide  expanse  of  ocean  almost  all  traces  of  the  present  physical 
geography  of  Europe  may  be  said  to  be  lost ;  for  since  Eocene 


FIG.    144. — BASALTIC  PLATEAUS  OF  THE  COIRON  IN  THE  ARDECHE. 

Here  the  underlying  beds  are  Jurassic,  but  the  lacustrine  have  thesame  effect. 

times  all  the  more  sharply  denned  mountain  systems  of  the  south- 
ern half  of  Europe  have  virtually  come  into  existence. 

A  brief  sketch  of  the  history  of  the  Alps  may  serve  to  indicate  a 
process  which  is  repeated  in  many  regions  of  the  earth.  During  the 
greater  part  of  the  Secondary  era  the  sea  flowed  where  the  Alps  now 
rise  ;•  the  vast  masses  of  limestones,  or  of  shaly  and  gritty  mudstones, 
which  more  especially  form  the  outer  zones  of  these  mountains, 
were  in  course  of  accumulation.  The  irregular  floor  on  which  they 
were  deposited  consisted  mainly  of  very  ancient  crystalline  rocks, 
with  which  locally  some  Primary  deposits  were  associated — these, 
however,  for  the  moment  may  be  passed  over.  In  places  parts  of 
this  floor  may  have  risen  in  islands  above  the  sea  level ;  but  this  can- 


410  THE   STORY  OF  OUR  PLANET. 

not  be  proved,  and  the  evidence,  so  far  as  it  goes,  is  unfavorable  to 
the  idea.  Disturbances  appear  to  have  been  first  felt  in  the  extreme 
east  of  the  Alpine  region,  and  the  ground  there  may  have  emerged 
from  the  sea  rather  before  the  end  of  the  Secondary  era ;  but,  as  a 
whole,  the  Alps  were  not  until  the  end  of  the  Eocene.  Along  the 
northern  zone,  and,  to  some  extent,  on  the  southern  also,  a  very 
thick  shaly  or  sandy  deposit,  called  the  Flysch,*  may  be  traced, 
which  seems  to  indicate  a  westward  traveling  of  similar  physical 
conditions;  for  in  the  one  locality  it  begins  in  Cretaceous  times,  and 
in  the  other,  starting  later,  it  concludes  early  in  the  Oligocene.  All 
the  beds,  up  to  the  age  of  the  later  Eocene  strata  of  Britain,  are 
affected  by  the  great  processes  of  folding  which  made  the  Alps. 
The  first  of  these  produced  a  mountain  chain,  probably  not  less 
elevated  than  the  present  one,  the  structure  of  which  may  have 
resembled  that  of  the  Eastern  Tyrol,  viz.,  a  chain  composed  of  three 
ranges,  of  which  the  central  was  the  most  strongly  marked  and 
formed  the  watershed.  In  speaking  of  the  formation  of  a  mountain 
chain  taking  place  at  a  certain  epoch  we  do  not  mean  to  imply  that 
the  event  was  sudden,  as  man  counts  time.  Probably  the  area  began 
to  move  much  before,  and  continued  to  move  long  afterward  ;  but 
it  appears  as  if  there  were  occasional  epochs  when  the  changes  were 
more  rapid,  and  these  conveniently  may  be  taken  as  dates.  From 
early  in  the  Oligocene  to  the  end  of  the  Miocene  denudation  in  the 
mountain  regions  and  deposition  on  its  marginal  zones  progressed 
pari passu,  until  another  period  of  intense  movement  began,  which 
seems  to  have  affected  mainly  the  Central  and  Western  Alps.  As 
a  consequence,  probably,  of  this,  a  marked  change  may  be  observed 
in  the  orography  of  the  Alps.  East  of  the  upper  valley  of  the  Inn 
the  central  range  forms  the  watershed  ;  but  that  river,  with  the 
Rhine,  the  Reuss,  and  the  Rhone,  appears  to  start  from  the  northern 
face  of  the  southern  range,  which  continues  to  be  the  watershed 
until  the  Alps  are  lost  in  the  Apennines.  Simultaneously,  however, 
with  this  change  the  northern  range  becomes  orographically  of 
greater  importance,  and  it  is  flanked  in  Switzerland  by  an  outer  zone, 
including  the  Rigi  and  the  Speer,  which,  as  already  mentioned,  can- 
not be  much  earlier  in  date  than  the  end  of  the  Miocene  period. 
In  the  Bernese  Oberland — the  grandest  part  of  the  northern  range — 
the  most  extraordinary  contortions  may  be  observed,  ridges  of  the 


*  In  places  this  deposit  contains  some  erratic  blocks,  remarkable  both  for  quantity   and 
for  their  occasional  size. 


THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS.        411 

older  rocks  in  many  places  being  bent  over,  or  even  thrust  forward 
above  masses  of  later  date.  This  set  of  disturbances  appears  to 
have  affected  the  whole  region — at  least  as  far  as  Dauphine.  The 
massif  of  the  Pelvoux  and  Ecrins,  the  ridges  of  the  Grandes 
Rousses  and  Belledonne,  occupy  positions  similar  to  that  of  the 
Bernese  Oberland,  and  both  ranges  appear  to  be  connected  with  and 
to  culminate  in  the  chain  of  Mont  Blanc.  Throughout  this  region, 
with  one  exception,  the  drainage  is  discharged  northward  or  west- 
ward, all  the  rivers  ultimately  reaching  the  Rhine  or  the  Rhone, 
chiefly  the  latter.  The  only  water  that  finds  its  way  to  Italy  is  from 
the  southern  side  of  Mont  Blanc  ;  perhaps  the  exceptional  elevation 
of  this  massif  may  have  had  the  result  of  enlarging  the  area  drained 
by  the  Dora  Baltea,  and  thus  changing  for  a  short  space  the  posi- 
tion of  the  watershed  of  Europe.  When  first  the  valley  of  the 
Upper  Rhone  was  sketched  out,  the  northern  range  very  probably 
resembled  that  which  forms  the  frontier  of  the  Tyrol  and  of  Bavaria, 
and  had  been  already  gashed  by  the  river,  which,  if  the  ground  rose 
gradually,  would  still  be  able  to  saw  for  itself  a  passage,  so  that  the 
main  outlines  of  the  physical  geography  of  the  region  would  not  be 
disturbed.* 

The  history  both  of  the  Apennines,  on  one  side  of  the  Adriatic, 
and  of  the  mountains  of  Istria,  Dalmatia,  and  Montenegro  on  the 
other,  cannot  be  separated  from  that  of  the  Alps.  In  them  also 
indications  of  a  shallowing  sea  are  given  by  the  Eocene  deposits  ; 
the  elevation  into  mountain  ranges  or  chains  is  approximately  con- 
temporaneous with  the  movements  of  the  Alps.  The  Pyrenees, 
though  less  complicated  than  the  latter,  appear  to  have  a  like  his- 
tory. There  are  similar  marginal  conglomerates,  probably  about 
the  same  age  as  the  Swiss  nagelfluh,  and  evidence  may  be  obtained 
of  not  less  than  two  movements,  of  which  the  first  was  the  more 
important.  The  genesis  of  the  Carpathians  and  of  the  Caucasus 
was  probably  connected  with  the  same  series  of  earth  movements. 
In  all  these  cases  insular  tracts  of  land  may  have  previously  risen 
above  the  water,  or  even  mountains  have  occupied  part  of  the  site  in 
ages  long  remote ;  but  the  chains  did  not  begin  to  exist,  as  they  are 
at  present  developed,  until  the  end  of  Eocene  times. 

In  the  more  northern  part  of  Europe  the  interval  between  the 
Tertiary  and  Secondary  eras  appears  to  have  been  occupied  by 
denudation  rather  than  by  deposition,  though  at  Faxoe,  Maestricht, 

*  This  subject  and  other  points  in  the  history  of  the  Alps  are  discussed  by  the  author  in 
three  lectures,  published  in  the  Alpine  Journal \  vol.  xiv.  pp.  39,  105,  221. 


4"  THE   STORY  OF  OUR  PLANET. 

and  Meudon,  near  Paris,  beds  are  found  which  help  somewhat  in 
bridging  the  vast  gap,  which  in  most  parts  of  this  region  exists, 
between  the  top  of  the  Chalk  and  the  bottom  of  the  Eocene.  Here, 
on  the  whole,  a  larger  area  was  occupied  by  sea  in  the  Cretaceous 
than  in  the  Eocene  period,  and  the  evidence  suggests  that  first  a 
steady  rise,  and  then  a  less  marked  fall,  affected  a  very  considerable 
extent  of  country.  But  even  so  far  back  as  this  time  we  find  some 
hint  of  a  division  of  the  waters  along  the  line  of  the  German  high- 
lands, and  the  great  southern  ocean  seems  to  have  held  its  ground 
continuously  from  the  Secondary  to  the  Tertiary  era,  but  to  have 
become,  on  the  whole,  more  shallow  during  the  latter. 

During  the  Cretaceous  period  an  ocean,  studded  here  and  there 
with  islands,  occupied  the  place  of  Europe.  White  chalk,  identical 
with  that  of  England,  extends  eastward  for  a  long  distance  north  of 
the  line  joining  Brittany  with  the  Ardennes.  Probably  the  deposit 
once  covered  the  whole  area  to  beyond  the  Baltic,  and  stretched 
southward  from  the  55th  parallel  of  latitude  to  the  last-named 
regions  and  the  German  highland  ;  for  sands  partly  replace  it  at 
Aix-la-Chapelle,  and  coarse  sandstones  in  the  Saxon  Switzerland. 
The  sea  also  overflowed  the  southern  half  of  Russia,  and  a  large 
part  of  the  countries  bordering  the  present  Mediterranean,  beyond 
which  it  extended  eastward  into  Asia,  and  southward  into  Africa. 
True  chalk,  however,  was  only  formed  in  one  or  two  areas  of  Central 
and  Southern  Russia.  Limestones,  indeed,  are  frequent,  but  those 
of  Gascony  and  Provence,  of  the  Eastern  Alps,  and  the  mountains 
on  each  side  of  the  Adriatic  are  pure,  but  hard,  furnishing  very  fine 
building  stone,  the  fossils  indicating  different  conditions  and  a  partial 
separation  from  the  northern  seas.  In  the  Central  and  Western 
Alps  the  limestones  are  often  less  clean,  or  replaced  by  other  sedi- 
ments. Probably  they  were  formed  in  comparatively  shallow  water, 
and  here  and  there  actual  fluviatile  deposits  occur,  as  in  Provence 
and  Carinthia,  Istria  and  Dalmatia,  and  the  Bakony.  But  there  can 
be  little  doubt  that  during  the  Cretaceous  period  the  European 
area,  as  a  whole,  was  depressed  more  widely  and  extensively  than 
even  in  the  Eocene,  or  than  in  any  other  part  of  the  Secondary  era. 

The  Neocomian  period  in  Europe,  as  in  England,  indicates  more 
varied  conditions,  and  a  gradually  progressing  downward  movement. 
The  English  fresh-water  Weald  finds  a  counterpart  in  Northern 
Germany ;  *  the  two  may  have  been  connected,  but  the  German 

*  In  Hanover,  Brunswick,  the  Teutoburger  Wald,  etc. 


THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS.        413 

Weald  almost  certainly  must  have  been  deposited  by  a  different 
group  of  rivers.  Probably  they  flowed  from  the  mountain  region 
of  which  Scandinavia  is  a  fragment.  In  Spain  also  a  similar  group 
of  rocks  has  been  found,  but  in  the  area  north  of  the  present 
Mediterranean — the  Jura  and  the  Alps — marine  beds  are  well 
developed,  including  limestones,  which  sometimes  are  very  thick 
and  pure. 

In  the  Jurassic  period  the  sea  in  Europe  occupied  an  area  similar 
to,  but  more  restricted  than,  that  which  is  concealed  in  the  Creta- 
ceous; indeed,  the  bolder  physical  features  of  the  entire  region 
appear  to  have  remained  unchanged  throughout  almost  the  whole  of 
the  Secondary  era,  the  differences  being  mainly  due  to  the  greater  or 
less  extent  of  submergence.  The  English  gulf  was  only  a  prolonga- 
tion of  the  French  sea,  and  in  a  southeasterly  direction  the  sedi- 
mentary members  of  the  system  attenuate  and  the  calcareous 
increase.  The  Lias,  however,  of  North  Germany  and  of  the  Alps 
is  not  unlike  that  of  England,  though  in  the  more  eastern  part  of 
the  second  region  it  passes  into  massive  limestones,  and  indicates 
a  greater  distance  from  any  important  tract  of  land.  Jurassic 
deposits  cover  much  of  Northern  Russia,  and  may  once  have 
extended  over  most  of  the  country,  but  were,  perhaps,  interrupted 
by  islands  in  the  south  and  in  the  adjoining  part  of  Roumania  and 
Hungary. 

The  Triassic  deposits  express,  in  a  more  accentuated  form,  a  dis- 
tinction, of  which  some  trace  remains,  even  in  the  Jurassic  period, 
for  the  Franco-German  Trias  differs  widely  from  that  of  the  Alpine 
region.  The  former  is  closely  related  to  that  of  England ;  the 
deposits,  indeed,  in  Normandy  clearly  indicate  the  existence  of 
similar  conditions.  When  they  reappear  on  the  eastern  side  of 
France,  both  the  Bunter  and  the  Keuper  present  a  general  resem- 
blance to  the  contemporaneous  deposits  in  Britain,  but  here,  as,  for 
instance,  in  Alsace-Lorraine,  they  are  separated  by  a  group  of 
marine  origin,  generally  calcareous.  This  is  termed  the  Musch- 
elkalk,  but  of  it  no  trace  occurs  in  Britain.  In  the  Triassic  period 
probably  the  more  northern  part  of  the  European  area,  including 
much  of  Russia,  was  a  lowland  region,  occupied  by  the  deltas  and 
estuaries  of  rivers,  by  lakes,  or  by  seas,  which  were  almost,  if  not 
entirely,  cut  off  from  the  open  ocean. 

But  in  the  more  southern  part  very  different  conditions  prevailed. 
Early  in  the  Trias,  and  throughout  the  whole  period  in  some  places, 
a  highland,  if  not  a  mountainous,  region  occupied  the  site  of  the 


4t4  THE   STORY  OF  OUR  PLANET. 

Western  and  Central  Alps,  but  from  it  the  sea  deepened  rapidly 
eastward  and  southward.  Instead  of  the  sandy  Bunter  and  marly 
Keuper  of  the  northern  region,  we  find  in  the  Eastern  Alps  huge 
masses  of  limestone  and  dolomite,  very  probably  formed  by  coral 
reefs  and  their  debris.  From  these  the  grand  cliffs  and  towers  of 
the  Dolomite  Mountains  have  been  sculptured,  an  Alpine  region 
for  long  almost  unknown  to  English  travelers.  This  series  of  dis- 
tinctively marine  deposits  occupies  a  large  area  all  round  the  present 
Mediterranean  Sea,  and  extends  for  a  long  distance  into  Asia.* 

In  parts  of  Germany  and  in  Russia  the  break  between  Trias  and 
Permian  is  not  strongly  marked,  while  in  the  most  eastern  part  of 
the  Alps  the  latter  sometimes  rest  in  order  of  sequence  on  marine 
(upper)  Carboniferous  deposits.  In  this  district  obviously  marine 
conditions  were  persistent  for  a  long  period,  but  in  Europe,  as  in 
Britain,  the  physical  geography  of  very  considerable  regions  was 
profoundly  modified  at  the  close  of  the  epoch  when  the  Carbonif- 
erous system  was  deposited.  The  changes  will  be,  perhaps,  most 
readily  appreciated  if  we  give  a  brief  summary  of  the  geological 
record  from  the  beginning  of  the  last-named  period,  "generally 
marine  in  the  earlier,  and  fresh  water  in  the  later  part."  Through- 
out physical  conditions  similar  to  those  of  Britain  prevailed  over 
the  Franco-Belgian  area,  and  extended  more  or  less  interruptedly 
into  Russia.  The  southern  boundary  of  the  sea  is  roughly  indi- 
cated by  Brittany,  the  Auvergne  uplands,  and  the  Western  and 
Central  Alps — while  it  flowed  over  the  extreme  east  of  this  chain, 
and  covered  a  very  large  part  of  Russia.  But  in  other  parts  of  the 
Alps  beds  of  fresh-water  origin  may  be  found,  which  have  been 
formed,  as  in  Britain,  over  a  much  wider  area  than  the  marine 
deposits.  Here  a  highland,  if  not  a  mountain,  district  already 
existed,  in  which  dark  carbonaceous  rocks  were  formed,  these  some- 
times being  coarse  breccias  or  conglomerates,  but  sometimes  con- 
taining thin  seams  of  coal.  The  Carboniferous  period  over  a  large 
part  of  Europe  was  closed  by  a  great  series  of  earth  movements. 
The  crust,  not  only  in  Britain,  but  in  the  northern  half  of  France 
and  Germany,  was  bent  into  a  series  of  huge  folds,  the  axes  of  which 
extend,  roughly,  from  west  to  east,  and  the  Alpine  region  was  simi- 
larly affected.  Throughout  the  Permian  and  most  of  the  Trias  a 
large  part  of  this  region,  west  of  the  head  of  the  Rhone  valley,  was 

*  The  Rhaetic  beds  in  the  northern  area  resemble,  but  are  better  developed  than,  those 
of  England  ;  in  the  southern  they  are  mostly  dolomites,  like  the  representatives  of  the 
underlying  Keuper. 


THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS.        415 

a  mountainous  mass  of  land.  In  connection  with  these  flexures, 
perhaps  as  one  result  of  them,  volcanoes  broke  out  in  many  places; 
enormous  masses  of  lava  and  ash  were  discharged  in  parts  of  Central 
Germany,  as  Thuringia,  Saxony,  and  Bavaria,  of  Bohemia,  of  the 
Eastern  Alps,  and  for  some  distance  westward  along  the  southern 
margin  of  the  present  chain.  These  volcanoes  were  most  active  in 
the  earlier  part  of  the  Permian  period,  but  in  some  regions,  as  in 
the  Alpine  district  around  Predazzo,  they  were  not  extinct  even  in 
the  Triassic.  But  afterward,  throughout  the  whole  of  the  Secondary 
era,  Europe  was  practically  free  from  volcanic  disturbances.  In  the 
later  part  of  the  Permian  period  terrestrial  conditions  or  seas,  more 
or  less  separated  from  the  open  ocean,  seem  to  have  prevailed  north 
•of  the  Alps,  including  much  of  Russia,  so  that  the  history  of  this 
region  differed  but  little  from  that  of  Britain. 

If  a  line  be  drawn  roughly  across  Europe  from  the  Black  Sea  to 
the  North  Sea,  it  divides  the  continent  into  portions,  which,  after 
Carboniferous  times,  passed  through  very  different  phases.  On  the 
more  eastern  side  the  changes  were  comparatively  inconspicuous. 
The  deposits  indicate  an  oscillation  between  shallow  seas  or  salt 
lakes  and  low-lying  lands.  But  on  the  more  western  side  the  phys- 
ical geography  was  completely  revolutionized.  From  La  Vendee  to 
the  north  of  England,  from  the  coast  of  Kerry  to  the  neighbor- 
hood of  the  Elbe,  that  immense  group  of  flexures  has  left  its 
mark  on  all  the  Primary  rocks.  Its  effects  have  been  detected,  as 
already  stated  (p.  380),  in  borings  beneath  the  valley  of  the  Thames. 
The  buried  mass  shows  itself  from  under  the  Secondary  rocks 
between  Calais  and  Boulogne,  and  can  be  tracked  eastward  by  a  line 
of  collieries  through  Northern  France  into  Belgium.  To  these 
movements  we  owe  the  making  of  that  vast  highland  district  in 
which  the  glens  of  Kerry  and  the  ravines  of  the  Ardennes,  the  dales 
of  Yorkshire  and  of  Eastern  Belgium,  the  coast  scenery  of  Corn- 
wall and  Devon,  of  the  Channel  Isles  and  Brittany,  have  all  been 
sculptured.  In  the  Alps  also  the  Carboniferous  rocks  are  sharply 
infolded  among  the  crystalline  schists ;  and  in  more  than  one  place, 
as  at  the  base  of  the  Todi  or  in  the  valley  of  the  Upper  Romanche, 
the  lowest  Secondary  measures  may  be  seen  resting  on  the  denuded 
edges  of  the  broken  folds.  The  interval  between  the  later  Car- 
boniferous deposits  and  the  earliest  of  the  Trias  is  so  long  that  the 
flexures  which  differ  "in  direction  may  possibly  differ  in  date.  Men- 
tion has  already  been  made  of  this  in  regard  to  Britain.*  Some  of 

*  See  p.  370. 


41 6  THE    STORY  OF  OUR  PLANET. 

the  Alpine  flexures  also  appear  to  have  run  more  nearly  north  and 
south.*  But  be  this  as  it  may,  the  changes  in  the  northwestern 
and  west-central  regions  were  prodigious,  for  these  great  folds  not 
only  had  been  formed,  but  also  had  been  profoundly  sculptured 
before  Triassic  times.  Indications  of  this  are  afforded  in  Britain; 
they  are  even  more  striking  in  a  geological  map  of  France.  Brit- 
tany and  La  Vendee  are  composed  of  huge  folded  masses  of  Pri- 
mary and  Archaean  rock,  the  outcrops  of  which  trend  generally 
rather  to  the  south  of  east ;  on  that  side  they  are  buried  beneath 
Secondary  strata,  which  cross  them  almost  at  right  angles.  Hence 
not  only  must  the  upland  masses  on  both  sides  of  the  English 
Channel  have  been  formed,  but  also  the  broad  interval  between  the 
highlands  of  the  Ardennes  and  of  Armorica,  and  the  narrower  one 
between  the  latter  and  Auvergne,  must  have  been  excavated.  It 
was  not  so  much  a  change  as  a  revolution  in  physical  geography, 
which  in  many  parts  of  Europe  separates  the  last  record  of  the 
Primary  from  the  first  record  which  is  in  complete  continuity  with 
the  Secondary  era. 

In  pre-Carboniferous  times  it  becomes  more  and  more  difficult, 
owing  to  the  complexity  of  the  details,  to  tell,  in  a  few  words,  the 
story  of  the  making  of  Europe.  But  it  is  probable  that  the  crystal- 
line masses  of  Scandinavia  and  Brittany,  like  those  of  Scotland,  of 
Auvergne  and  the  Cevennes,  of  the  Vosges  and  Schwarzwald,  of 
Bavaria  and  Bohemia,  of  Spain  and  Portugal,  and  even  of  some 
parts  of  the  Alps  and  Pyrenees,  with  other  districts  near  the  Med- 
iterranean, severally  indicate  the  position  of  land  surfaces  from  a 
very  early  period  in  the  history  of  the  globe.  In  all  these  regions 
the  older  Primary  (or  Palaeozoic)  rocks  either  are  wanting  or,  if 
present,  are  evidently  shallow  water  deposits  infolded  among 
crystalline  schists  of  still  earlier  date. 

In  Devonian  times  a  sea,  with  which  that  of  Southern  England 
was  connected,  extended  over  much  of  Northern  France  and  Ger- 
many into  Russia.  In  the  northwest  of  the  last  region  the  associa- 
tion of  rocks  which  recall  the  Old  Red  Sandstone  type  of  Wales 
and  Scotland  with  marine  beds,  like  those  of  Devonshire,  indicates 
an  oscillation  between  marine  and  more  or  less  terrestrial  conditions. 
Indeed,  a  very  considerable  area  of  the  northern  half  of  Europe, 
including  much  of  Germany,  appears  to  have  been  occupied  by 
a  rather  shallow  land-girt  sea,  which  was  deepest  toward  the  middle 

*  Possibly  the  Ural  range  may  have  been  formed  at  this  period,  though  an  earlier  date  is 
assigned  to  it  by  some  geologists. 


THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS.        417 

of  the  period.  There  was  also  sea  in  the  neighborhood  of  the 
Eastern  Alps,  Bohemia,  and  Poland,  and  in  Spain,  with  Portugal. 

The  Cambrian,  Ordovician,  and  Silurian  deposits  of  Southern 
Scandinavia  and  the  adjacent  regions  of  Russia  are  unusually  thin 
and  unchanged,  being  in  places  still  comparatively  incoherent. 
From  this  we  should  conclude  that,  if  the  Scandinavian  region  even 
then  formed  a  shore  line  to  the  sea,  it  contributed  but  little  sedi- 
mentary material.  In  most  parts  of  Europe  limestones  are  not 
abundant  in  the  earlier  Primary  deposits  ;  muds  and  sands  indicate 
the  prevalence  of  physical  conditions  generally  similar  to  those  of 
the  British  Isles,  the  drift  of  sediment,  in  some  cases,  being  evi- 
dently from  the  west.  In  the  more  central  parts  of  Europe  beds  of 
Early  Primary  age  have  not  been  identified,  except  in  the  more 
eastern  portion  of  the  Alpine  region.  A  far-spreading  sea  evi- 
dently extended  from  the  British  Islands  across  Northern  France 
(so  as  to  include  Brittany),  Belgium,  the  hill  regions  of  Southern 
Prussia  (e.  g.,  the  Harz,  Thuringia,  etc.),  whence  it  most  probably 
stretched  across  Poland  and  overflowed  the  greater  part  of  Northern 
Russia  ;  perhaps  also  it  turned  southward  into  Bohemia.  Sea  also 
covered  Spain,  and  extended  during  part  of  the  time  eastward  as 
far  as  Sardinia,  but  there  is  no  evidence  that  this  was  connected 
with  the  more  clearly  defined  northern  marine  area.  The  fauna, 
and  to  some  extent  the  general  character  of  the  older  Primary 
deposits  in  Bohemia,  agree  more  nearly  with  those  of  Southern 
Europe  than  with  those  belonging  to  the  Anglo-Scandinavian  sea. 
In  Norway,  as  in  the  Scotch  Highlands,  beds  somewhat  older  than 
the  Cambrian  may  be  identified. 

To  conclude :  The  evidence  which  has  been  briefly  summarized 
indicates  that  many  of  the  European  highlands  have  existed,  as 
physical  features,  from  very  early  times;  that  the  present  Mediter- 
ranean is  a  remnant — perhaps  representative  of  the  deepest  parts — 
of  a  fairly  persistent  oceanic  area,  also  of  great  antiquity  and  of  wide 
extent ;  and  that  in  the  north-central  region  (including  much  of 
Russia),  defined  on  the  north  and  west  by  the  crystalline  masses  of 
Scandinavia,  Northern  Scotland,  and  Ireland,  with  possibly  the 
extremity  of  Cornwall  and  Brittany,  there  was  a  constant,  struggle 
for  mastery  between  sea  and  land,  the  former,  on  the  whole,  pre- 
dominating. Further,  it  may  be  inferred  that  in  this  region  the 
movements  in  a  downward  direction  produced  the  most  conspic- 
uous effects  during  the  Lower  Carboniferous,  the  Jurassic,  and  the 
Cretaceous  times,  while  in  Europe  generally  the  earth's  crust  was 


41 8  THE   STORY  OF  OUR  PLANET. 

most  markedly  folded  and  disturbed  at  the  end  of  the  Carbonifer- 
ous, of  the  Eocene,  and  of  the  Miocene  periods.  But  the  move- 
ments which  affected  Britain  at  the  beginning  and  at  the  end  of  the 
Silurian,  though  now  less  conspicuous,  owing  to  great  subsequent 
denudation,  were  probably  once  of  no  small  importance,  and  formed 
parts  of  flexures  which  extended  over  much  wider  areas.* 

At  the  present  time  the  Asiatic  continent  consists  of  three 
regions,  very  distinct  in  their  physical  geography — namely,  that  of 
the  southern  peninsulas,  that  of  the  central  mountain  chains  and 
elevated  plateaus,  closely  associated  with  which  are  some  well- 
marked  basins,  and  lastly,  that  including  the  northern  steppes  and 
plains.  Of  these  the  most  stupendous  in  its  features  is  also,  on  the 
whole,  the  most  modern.  Of  the  northern  plain  but  little  is  known, 
and  not  much  is  likely  to  be  ascertained  owing  to  the  vast  morasses 
(tundras]  and  the  forests  which  cover  so  much  of  the  Siberian  low- 
land, but  the  geology,  at  any  rate  in  the  more  western  part,  is  prob- 
ably related  closely  to  that  of  Russia  on  the  opposite  side  of  the 
Urals.  In  the  southern  steppes  various  Primary  rocks  come  to  the 
surface,  but  there  are  few  or  none  of  later  date,  so  that  much  of 
Southern  Siberia  has  been  a  land  mass  continuously  from  very 
ancient  days,  and  almost  all  was  above  water  in  the  Tertiary  era. 

But  during  much  of  the  time  the  region  to  the  south  of  this,  the 
great  zone  of  mountains  and  plateaus,  was  under  water;  though  in 
the  peninsula  of  Hindustan  we  find  traces  of  a  very  ancient  land 
mass,  of  which  Ceylon  formed  a  part.  Large  areas  are  occupied  by 
crystalline  rocks  and  schists,  probably  Archaean,  which  here  and 
there  are  overlain,  especially  in  the  south,  by  tracts  of  Primary  rock. 
North  of  this  region  a  sea,  in  Secondary  and  earlier  Tertiary  times, 
appears  to  have  overspread  the  area  now  occupied  by  the  greatest 
mountain  masses  in  the  world.  To  this  sea  we  have  already  referred.f 

*  The  disturbances  which  have  affected  the  European  regions,  with  other  portions  of 
the  globe,  were  worked  out  in  much  detail  by  the  late  Professor  E.  de  Beaumont,  and 
a  revised  account  of  his  results  is  given  by  Professor  Prestwich  ("  Geology,"  part  i. 
ch.  xvii.).  But  the  genesis  of  mountain  chains  was  certainly  a  more  complicated  process 
than  the  former  supposed,  so  that  I  have  preferred  to  direct  attention  only  to  the  more 
important  and  best  established  movements.  When  we  find  that  a  comparatively  modern 
chain,  like  the  Alps,  is  the  result  of  at  least  two  fairly  distinct  sets  of  movements  in  the 
same  general  direction,  and  has  incorporated  with  it  fragments,  as  they  may  be  called,  of 
earlier  mountain  masses,  themselves  produced  by  more  than  one  set  of  disturbances,  acting 
apparently  by  no  means  in  the  same  direction,  we  begin  to  realize  how  complicated  these 
questions  speedily  become,  and  how  much  more  evidence  must  be  obtained  before  the 
puzzling  record  of  ancient  physiography  can  be  fully  deciphered, 

|Pp.  409,  412. 


THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS.        419 

It  extended  from  Central  Europe  across  Syria,  Asia  Minor,  Persia, 
and  the  whole  region  of  Northern  India,  Thibet,  and  Western  Mon- 
golia. Here  and  there  deposits  of  the  Primary  era  may  be  detected, 
but  very  often  deposits  of  Secondary,  occasionally  even  of  Tertiary, 
age  rest  on  ancient  crystalline  rocks.  This  is  the  case  in  Syria  and 
in  parts  of  Arabia,  Persia,  etc.,  and  among  the  Himalayas  and 
Karakorams  Secondary  and  Early  Tertiary  sediments,  as  in  the 
Alps,  are  infolded  with  rocks  presumably  Archaean  in  age.  The 
bed  of  this  sea,  as  already  said,  has  been  elevated  in  places  full 
16,000  feet  since  the  end  of  the  Eocene  period.  When  the  sea 
existed,  China,  like  most  of  India,  may  have  formed  land.  Here 
also  old  crystalline  rocks  and  schists  are  found ;  these  apparently 
sank  down  gradually  during  the  Primary  era,  for  among  them  are 
deposits  of  various  ages  till  somewhat  later  than  the  Carboniferous 
period.*  Volcanic  rocks  are  rather  abundant,  while  the  curious 
deposit  called  loess f  covers  large  districts.  On  the  whole,  it  is 
probable  that  the  great  belt  of  water  which  once  crossed  Asia  and 
united  the  Atlantic  with  the  Pacific  passed  in  the  direction  of 
Burmah  and  Siam,  where  newer  rocks  seem  to  exist.  Even  after 
the  great  Central  Asian  chains  were  formed,  a  shallow  sea  still 
separated  for  a  time  their  southern  slopes  from  the  Central  Indian 
land,  but  it  gradually  retired  when  the  great  detrital  deposits  of  late 
Miocene  or  Pliocene  age  were  upheaved,  as  also  happened  on  the 
borders  of  the  Alps. 

The  information  in  our  possession  is  insufficient  to  elucidate  the 
complexities  of  the  mountain  region  of  Central  Asia.  Its  connec- 
tion with  Europe  is  indicated  by  the  plateaus  and  ranges  of  Turkey 
in  Asia  and  of  Persia,  and  by  the  more  sharply  defined  chain  of  the 
Caucasus,  but  the  mass  rises  more  grandly  as  it  approaches  the 
Pamir  plateau,  "the  roof  of  the  world,"  and  forks  out  thence  like 
the  fingers  of  a  hand.  Baron  von  Richthofen,  in  his  classic  work 
on  China,  distinguishes  the  following  mountain  systems  in  the  mid- 
Asiatic  region.  Commencing  from  the  south,  they  are  : 

(i)  The  Himalayan  system  (including  the  Karakorams).  The 
axes  of  this  run  toward  the  southeast,  in  the  neighborhood  of  the 
Pamir  plateau,  and  gradually  curve  round  to  the  east  as  the-  ranges 
approach  the  longitude  of  the  Lower  Ganges.  As  the  Indus  and 
Brahmapootra  rise  at  the  base  of  the  Karakoram  chain,  and  run  for 


*  The  coal  fields  of  this  age  are  no  less  extensive  than  valuable, 
f  P.  91.     See  also  Geological  Magazine,  1882,  p.  293. 


420  THE   STORY  OF  OUR  PLANET. 

a  long  distance  respectively  west  and  east  between  it  and  the  Hima- 
layas before  cutting  through  the  latter,  it  is  clear  that,  as  in  the  case 
of  the  Bernese  Oberland,*  the  first-named  chain  is  the  older,  and 
that  this  system  is  the  result  of  more  than  one  set  of  movements. 

(2)  The  Kuenlun  system,  the  axes  of  which  run  slightly  to  the 
south  of  east. 

(3)  The  Thian-Shan  system,  the  axes  of  which  run  approximately 
E.N.E.     Seemingly  connected  with  this  are  not  only  the  mountain 
chains  which  extend  far  in  the  direction  of  Southern  Siberia,  but 
also  the  massifs  to  the  southwest  of  the  Pamir  region,  of  the  Hindu- 
Khush  and   other  ranges  in  Persia,  Afghanistan,  and  Beluchistan. 
If  so,  this  system  is  geographically  of  the  greatest  importance,  for  it 
may  be  said  to  extend  almost  from  the  Arabian  Sea  to  Behring 
Strait. 

(4)  The  Altai  system  has  an  E.S.E.  trend,  and  seems  in  places 
to  inosculate  with  or  intrude  upon  that  of  the  Thian-Shan.     This 
set  of  disturbances  also  affects  a  large  zone,  generally  on  the  western 
side  of  the  later  system,  and  is  continued  in  the  ranges  about  the 
head  waters  of  the  Amu  Daria  and  Syr  Daria,  as  far  as  the  mouth 
of  the  Persian  Gulf. 

(5)  The  Chinese  system  has  a  northeastern  trend,  and  affects  the 
regions  on  both  sides  of  the  Kuenlun,  and  so  eastward  into  China 
proper. 

(6)  The  "  Hinter  "  Indian  system,  which  runs  through  Burmah  to 
the  Malayan  Peninsula,  trends  rather  to  the  east  of  south.     This 
seems  to  inosculate  with  the  Himalayan  system,  very  much  (to  com- 
pare small  things  with  large)  as  do  the  mountains  of  Dalmatia  and 
Istria  with  the  eastern  portion  of  the  main  Alpine  chain. 

It  would  be  rash  at  present  to  attempt  to  indicate  the  relations 
or  exact  ages  of  these  chains ;  but  the  fact  that  not  only  some 
Primary  and  Secondary,  but  also  Early  Tertiary,  strata  occur  imme- 
diately west  of  the  Thian-Shan,  about  Lake  Issyk-Kul,  and  in  the 
mountain  plexus  northwest  of  the  Pamirs,  makes  it  probable  that 
most,  if  not  all,  these  chains,  in  their  present  form,  are  no  older  than 
the  Alps,  though,  like  them,  they  may  include  remnants  of  earlier 
mountain  regions.  Among  them,  as  already  stated,  are  some  of  the 
loftiest  summits  in  the  world,  the  highest  peaks  being  in  the  Hima- 
layan system;  but  points  in  the  Hindu-  Khush,  the  Kuenlun,  and 
Thian-Shan  chains  sometimes  rise  well  above  20,000  feet.  The 

*P.  411. 


THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS.        421 

plateau  of  Thibet  is  generally  full  12,000  feet  above  sea  level,  and 
that  of  Gobi  some  4000  feet.  The  uplift  of  this  vast  central  region 
seems  to  have  determined  the  course  of  the  chief  rivers  of  Asia. 
The  middle  portion,  between  the  Karakorams  and  the  Thian-Shan, 
on  each  side  of  the  Kuenlun  chain,  is  a  region  of  inland  drainage ; 
then  from  its  eastern  side  the  waters  flow,  often  rather  circuitously, 
to  the  Pacific  coast.  The  Black  Sea,  the  basins  of  the  Caspian  and 
the  Sea  of  Aral  receive  most  water  from  Russia  and  Western 
Siberia,  but  as  the  flanks  of  the  Thian-Shan  are  approached  the 
rivers  begin  to  take  a  northward  course  to  the  Arctic  Ocean.  The 
fact  that  in  Southern  Hindustan  the  main  rivers  rise  on  the  flanks 
of  the  Western  Ghauts,  and  cut  through  the  Eastern  Ghauts  on  their 
way  to  the  Bay  of  Bengal,  indicates  the  superior  antiquity  of  the 
former  range. 

The  long  chain  of  volcanic  islands  which  borders,  though  at  a 
distance,  most  of  the  eastern  coast  of  Asia,  and  the  fact  that  the 
crystalline  schists,  etc.,  which  form  part  df  the  mountains  of  Japan 
bear  signs  of  intense  pressure,  indicate  that  along  the  western  zone 
of  the  Pacific  Ocean  folds  have  been  forming,  and  the  frequent 
eruptions  and  earthquake  shocks  suggest  that  the  process  has  hot 
yet  ended. 

The  geology  of  vast  regions  in  Africa  is  still  a  blank,  though 
during  the  last  twenty  years  our  knowledge,  both  in  the  north  and 
south,  has  been  much  augmented.  What  has  been  said  of  Western 
Asia  applies  generally  to  Egypt  and  to  a  considerable  tract  inland 
from  the  north  coast  of  Africa.  This  was  once  overflowed  by  an 
ocean  of  which  the  Mediterranean  Sea  is  a  remnant.  But  during 
much  of  the  Primary  and  Earlier  Secondary  time  a  great  part  of 
Northern  Africa  was  probablyiabove  water,  for  over  a  large  area 
nothing  is  found  (except  some  small  patches  of  Carboniferous  rocks) 
older  than  Jurassic  time,  and  in  many  places  a  sandstone,  slightly 
earlier  in  date  than  the  Chalk  of  England,  rests  upon  crystalline 
schists  or  igneous  rocks  of  great  antiquity.  After  these  times  it 
was  overflowed  by  the  sea,  which  already  has  been  mentioned.  The 
Atlas  range,  which  forms  a  southern  boundary  of  this  region,  con- 
sists of  a  crystalline  axis  followed  by  masses  of  eruptive  igneous 
rock,  and  by  sedimentary  deposits,  probably  of  later  Secondary  age. 
The  date  of  its  upheaval  seems  to  be  uncertain,  but  most  probably 
it  is  coeval  with  that  of  the  Alps.  In  the  more  central  regions,  such 
as  Abyssinia  and  that  about  the  White  and  Blue  Nile,  we  still  find 
a  floor  of  crystalline  rock  overlain  by  sediments,  such  as  Jurassic 


422  THE   STORY  OF  OUR  PLANET. 

limestones,  and  sandstones  of  an  earlier  age.  The  Tertiary  sea  may 
have  overflowed  for  a  time  the  eastern  side  of  the  continent  as  far 
as  Somaliland,  but  a  very  large  part  of  Central  Africa,  including 
almost  all  that  lies  to  the  south  of  the  fifth  parallel  of  north  latitude 
(the  narrower  portion),  consists  of  rocks  of  either  Primary  or  Early 
Secondary  age,  beneath  which  a  crystalline  floor  is  sometimes 
exposed.  South  of  the  Orange  and  Limpopo  rivers  we  find  but 
little  that  is  later  than  the  earliest  part  of  .  the  Jurassic  period, 
Triassic  rocks  occupying  considerable  areas.* 

Active  volcanoes  or  lofty  mountain  chains  are  almost  entirely 
absent  from  Africa ;  the  highest  summits  are  indeed  volcanic,  but 
their  fires,  as  at  Kilimanjaro,  Keenia,  and  Ruwenzori,  are  generally 
extinct.  The  most  mountainous  ground  is  often  near  the  coast, 
much  of  the  interior  being  a  fairly  elevated  hilly  plateau,  often 
averaging  4000  feet  above  the  sea.  The  highest  summits  of  the 
Atlas  may  reach  about  12,000  feet,  but  in  other  parts  of  Africa  if 
anything  rises  above  sorrfe  10,000  feet  it  is  a  volcanic  cone,  f  In 
many  districts  igneous  rocks  are  interbedded  with  or  break  through 
stratified  deposits  of  various  ages. 

The  courses  of  the  great  rivers  of  Africa  are  remarkable,  and 
suggest  the  possibility  of  the  continent  being  formed  by  the  combi- 
nation of  a  series  of  masses  originally  insulated.  The  elevated  lake 
region  of  Central  Africa,  the  physical  history  of  which  has  not  yet 
been  investigated,  sends  off  the  Nile  system  to  the  north,  the 
Congo  system  to  the  west,  and  the  limited  Shire  to  the  south. 
Occupying  the  angle  between  the  basins  of  the  first  and  the  second 
is  a  large  area  of  inland  drainage,  to  which  succeeds  the  basin  of  the 
Niger.  Both  this  river  and  the  Congo  follow  rather  singular  paths; 
the  latter  one  sweeps  northward  in  a  great  curve  to  beyond  the 
equator,  and  then  returning  reaches  the  sea  more  than  five  degrees 
south  of  it.  The  Niger,  rising  not  very  far  from  the  west  coast, 
runs  eastward  and  then  southward,  to  flow  at  last  into  the  Gulf  of 
Guinea.  Thus  the  Kong  and  Saraga  mountains  on  the  north  of 
that  gulf  and  the  Sierra  Complida  on  the  east  of  it  seem  to  have 


*  The  celebrated  diamond  mines  of  Kimberley  are  in  the  Karoo  shales,  which  belong  to 
the  Trias.  Some  igneous  rocks  have  broken  into  these  shales,  and  the  diamonds  are 
found  in  rude  circular  areas,  which  appear  to  have  been  somewhat  affected,  perhaps  by 
water  or  by  steam. 

t  The  height  of  Kilimanjaro  is  19,680  feet,  of  Keenia  about  18,000  feet,  and  of  Ruwen- 
zori nearly  the  same.  The  Cameroons,  near  the  Gulf  of  Guinea,  are  about  13,700  feet, 
and  are  also  volcanic, 


THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS.        423 

diverted  the  rivers  from  their  natural  courses.  South  of  the  out- 
let of  the  Congo  is  another  mountainous  mass,  similar  to  that 
last  named.  Its  importance  seems  to  be  indicated  by  the  long 
course  of  the  Zambesi,  to  which  it  contributes ;  and  the  inland 
basin  of  Lake  Ngami  possibly  marks  the  position  of  a  channel 
which  once  separated  this  Angola  district  from  the  uplands  of  the 
central  lake  region.  South  of  the  Limpopo  the  mountains  of  the  east 
coast  become  dominant,  and  the  main  flow  of  water  is  westward. 
The  curiously  even  outline  of  the  whole  African  continent  south  of 
latitude  30°  N.  suggests  that  for  a  considerable  time,  geologically 
speaking,  it  has  undergone  but  little  disturbance. 

The  physical  structure  of  North  America,  on  the  whole,  is  more 
simple  than  that  of  Europe.  Much  of  the  continent  is  a  vast  hilly 
plateau,  which  occupies  all  the  northern  region,  except  for  a  certain 
distance  on  the  western  side,  and  which  gradually  sinks  down  to  the 
wide  plains  drained  by  the  Mississippi  and  its  tributaries.  These 
gradually  contract  toward  the  south,  ultimately  ending  on  the  shore 
of  the  Gulf  of  Mexico.  This  region  of  upland  and  plain  is  separated 
from  the  Atlantic  by  an  ancient  mountain  chain,  from  the  Pacific 
by  one  of  grander  size,  more  complex  structure,  and  more  modern 
date.  Thus  the  continent  consists  of  three  rather  distinct  regions, 
each  of  which  we  proceed  briefly  to  describe. 

In  the  northern  or  northeastern  region  Greenland  and  all  the  islands 
on  the  American  side  of  the  Arctic  Ocean  may  be  included.  Here, 
over  a  large  area  all  about  Hudson's  Bay,  the  rock  for  hundreds  of 
square  miles  is  mostly  Archaean — gneisses,  schists,  and  igneous 
masses  of  great  antiquity.  These,  however,  in  many  places,  espe- 
cially toward  the  southern  side,  are  overlain  by  Cambrian,  Ordovi- 
cian,  Silurian,  and  occasionally  even  later  rocks  of  the  Primary 
series.  The  first  occupies  the  most  limited  areas,  but  rocks  of  yet 
earlier  date  (Huronian)  also  occasionally  occur.  This  region,  as  a 
rule,  is  not  much  affected  by  great  dislocations,  sharp  folds,  or  other 
indications  of  severe  pressure.  The  sedimentary  deposits  seem  to 
succeed  one  another  with  tolerable  uniformity.  Among  them  the 
Trenton  limestone  (about  the  age  of  the  Bala  beds  of  Britain)  and 
the  Niagara  limestone  (the  equivalent  of  the  Wenlock)  are  thick 
masses  of  pure  calcareous  rock,  indicating  long-continued  accumu- 
lation in  quiet  seas  teeming  with  life.  Here,  then,  we  have  the  core 
of  the  American  continent — a  comparatively  undisturbed  portion  of 
a  region  which  at  a  very  early  epoch  was  above  water,  for  a  time 
oscillated  between  land  and  shallow  seas,  and  gradually  returned  to 


424  THE    STORY  OF  OUR  PLANET. 

its  former  condition.  So  far  as  we  can  judge  from  what  has  been 
revealed  by  the  gre?,.t  earth  movements  on  the  western  side  of 
America,  these  crystalline  rocks  continued  to  form  a  land  surface 
there  till  rather  late  in  the  Primary  era,  for,  as  a  rule,  the  earlier 
representatives  of  that  era  are  not  very  common,  and  in  some  cases 
strata  of  Secondary  age  rest  directly  on  rocks  presumably  Archaean. 
In  the  more  southern  part  of  Canada  and  in  the  Eastern  States 
the  history  of  the  region  in  the  Carboniferous  period  seems  to  have 
been  very  much  the  same  as  that  of  England  ;  alike  in  the  lower 
and  upper  part,  in  the  Limestone  and  the  Coal  Measures,  there  is 
great  similarity.  As  in  Europe,  so  here,  that  period  appears  to  have 
ended  with  an  epoch  of  severe  disturbance.*  A  mighty  thrusting 
force,  acting  apparently  from  the  direction  of  the  present  bed  of  the 
Atlantic,  formed  the  great  group  of  flexures  which  gave  rise  to  the 
Appalachians,  Alleghany,  and  other  ranges  bordering  the  Atlantic 
from  Alabama  to  Newfoundland.  By  these  movements  the  eastern 
coast  of  the  American  continent  was  denned.  Only  along  a  narrow 
littoral  strip  in  the  States,  and  over  a  rather  larger  area  of  compara- 
tive lowland  about  the  Gulf  of  Mexico,  have  any  important  addi- 
tions been  made.  During  the  Triassic,  and  even  the  Jurassic,  period 
this  continental  region  extended  very  far  west,  almost  to  the  Pacific 
coast,  though  in  the  latter  system  deposits  are  found  which  indicate 
that  the  sea  occasionally  trespassed  for  a  considerable  distance 
inland.  This,  however,  is  true  of  the  more  southern  rather  than  of 
the  more  northern  region.  Professor  Dana  believes  the  first  devel- 
opment of  the  Sierra  Nevada  as  a  mountain  range  to  date  from  the  end 
of  the  Jurassic  period,  after  which  time  a  downward  movement  began, 
so  extensive  as  to  affect  North  America  generally,  west  of  a  line  run- 
ning roughly  from  Lake  Winnipeg  to  Texas.  As  a  result,  almost 
the  whole  of  this  region  was  covered  by  a  shallow  sea,  the  bed  of 
which  slowly  sank.  In  this  the  great  masses  of  sediment  were 
deposited,  which  are  now  upraised  in  the  mountain  regions  of  the 
Western  States.  "  As  the  era  drew  toward  its  close,  the  subsidence 
appears  to  have  intermitted  for  long  intervals,  with  perhaps  some 
upward  movements,  so  that  the  land  became  slightly  emerged. 
Later,  the  eras  of  intermitted  subsidence  became  greatly  prolonged, 
so  that  immense  peat  beds  were  formed  from  the  vegetation  grow- 
ing over  the  quiet  marshes ;  but  between,  in  the  intervening  eras, 


*  It  is  stated  that  there  were  some  important  disturbances  in  the  Green  Mountain  region 
between  the  Ordovician  and  Silurian. 


THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS.        4*5 

during  which  the  sinking  was  renewed,  thick  sand  beds  and  clay 
beds  were  made,  containing  marine  or  fresh-water  shells,  or  both 
commingled.  .  .  Thus  gradually,  so  far  as  rock  making  was  con- 
cerned, the  Cretaceous  era  ended  and  the  Tertiary  age  began."  * 

Gradually,  toward  the  end  of  the  Eocene,  this  period  of  quiet 
movement,  of  deposition  mainly  terrestrial,  came  to  an  end,  and  the 
development  of  the  vast  mountain  region  of  the  West  began.  This 
was  a  protracted  process,  but  in  it  epochs  of  greater  intensity  have 
been  noted.  The  first  appears  to  have  occurred  early  in  the  Eocene 
period,  since  it  disturbs  the  Laramie  and  earlier  deposits  in  two  dis- 
tant regions,  one  west  of  the  Sierra  Nevada,  the  other  east  of  the 
Wahsatch.  The  second  epoch  closed  the  Eocene,  and  practically 
defined  the  eastern  half  of  America,  for  there  marine  Miocene  deposits 
are  restricted  to  the  Atlantic  border.  By  these  movements  also 
the  Rocky  Mountain  regions  were  affected,  but  not  very  greatly. 
The  third  epoch  closed  the  Miocene,  uplifted  yet  more  a  vast  area 
in  the  Rocky  Mountain  region,  and  produced  the  Coast  Range,  par- 
allel with  the  Sierra  Nevada.  During  the  Miocene  period  "  there 
is  proof  that  mountain-making  pressure,  from  the  Pacific  direction, 
had  acted  with  energy  against  the  continental  crust,  in  the  occur- 
rence of  extensive  areas  of  igneous  rocks  over  the  Pacific  slope  and 
part  of  the  summit  region,  and  the  vast  areas  of  trachyte  and  doler- 
ite  show  that  immense  regions  were  flooded  by  outpourings  from 
fractures  at  successive  times.  These  eruptions  continued  to  take 
place  over  those  regions  at  intervals  from  the  close  of  the  Miocene 
even  into  the  Quaternary  age,  and  they  have  not  even  now  alto- 
gether ceased."  f  It  must  not  be  forgotten  that  the  great  volcanic 
outbursts,  which  affect  the  region  from  Western  Greenland  to  Scot- 
land, and  even  to  Northern  Ireland,  were  also  of  Tertiary  age,  or  that 
the  submarine  plateau  which  runs  beneath  the  Faroes  and  Iceland 
appears  to  have  formed  for  a  considerable  time  a  link  of  land 
between  the  northern  continents  of  the  Old  and  New  World,  and  to 
have  parted  the  Arctic  from  the  Atlantic  Ocean. 

Thus  the  river  systems  of  Western  America,  like  most  of  those 
in  Europe,  date  from  the  later  part  of  the  Tertiary  era.  That  of 
the  St.  Lawrence  may  probably  claim  a  greater  antiquity,  and  so 
possibly  may  some  part  of  the  Mississippi.  During  the  Glacial 
epoch  a  great  ice  sheet  covered  most  of  Canada  and  much  of  the 

*  J.  D.  Dana,  "  Manual  of  Geology,"  p.  520,  second  edition, 
f  J.  D.  Dana,  "Manual,"  p.  524. 


426  THE   STORY  OF  OUR  PLANET. 

northern  States,  and  its  moraines  have  been  identified  by  American 
geologists,  in  some  places,  to  the  south  of  the  4<Dth  parallel  of 
latitude.*  The  continent  has  not  been  at  rest  since  the  process  of 
mountain  making  ceased,  for  there  has  been  considerable  depression 
in  the  lake  region  of  Canada  and  the  United  States,fand  the  deeply 
submerged  channels  of  the  St.  Lawrence,  the  Hudson,  and  other 
rivers  of  the  eastern  coast  indicate  that  this  region,  probably  during 
some  part  of  the  Glacial  epoch,  was  upraised  at  least  2000  feet 
above  its  present  level.  Still  the  continent  of  America,  as  a  whole, 
appears  to  have  been  little  changed  since  the  beginning  of  the 
Pliocene  era,  and  the  geography  of  all  its  northern  portion,  if  no 
more,  indicates  that  at  the  present  time  the  level  of  the  land 
generally  is  lower  than  when  its  chief  physical  features  were 
sculptured. 

The  South  American  continent  slightly  resembles  that  of  Africa 
in  outline,  though  on  the  whole  it  has  a  simpler  structure.  The 
Caribbean  Sea,  with  its  chain  of  islands  as  an  eastern  boundary, 
suggests  some  analogy  with  the  Mediterranean ;  the  land  link 
between  the  southern  and  the  northern  continents,  geologically 
speaking,  is  comparatively  recent,  and  the  date  of  the  final  severance 
between  Atlantic  and  Pacific  water  is  still  a  matter  of  dispute. 
Much  yet  remains  to  be  learnt  of  the  geology  of  this  continent,  but 
some  facts  of  great  importance  are  now  fairly  certain.  The  chain 
of  the  Andes  forms  part  of  that  group  of  flexures  which  borders 
the  Eastern  Pacific  from  north  to  south.  Yet  though  so  stupendous 
a  feature  in  the  continent,  it  is  comparatively  modern.  One  much 
more  ancient  is  indicated  by  the  great  plateau  of  Brazil,  which 
stretches  inland  from  the  Atlantic  as  far  as  the  Selvas  of  the 
Amazon  on  the  north,  and  the  Pampas  of  the  Rio  de  la  Plata  on 
the  west4  It  consists  mainly  of  ancient  crystalline  rocks,  covered 
in  places  by  Primary  strata.  The  plateau  of  Guiana  also,  between 
the  Amazon  and  the  Llanos  of  the  Orinoco,  is  a  smaller  mass  of 
like  composition.  As  there  are  some  indications  that  the  Primary 
strata  cross  the  Amazon  valley,  these  two  plateaus,  at  an  earlier 
period  of  their  history,  possibly  may  have  formed  a  single  conti- 
nental mass.  This,  no  doubt,  had  its  disturbances  in  days  of  old, 
bwt  for  ages  it  has  been  comparatively  at  rest,  and  the  scene  of 

*In  one  place  it  came  almost  50  miles  south  of  lat.  38°. 
f  Page  140. 

t  The  Selvas  are  forest-clad  lowlands,  the  Pampas  and  the  Llanos  grassy  lowlands  in  the 
several  river  basins. 


THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS.        427 

action  has  been  shifted  to  the  other  side  of  the  continent.  Here 
huge  volcanoes,*  often  rising  from  17,000  to  more  than  20,000  feet 
above  the  sea,  crest  the  chain  of  the  Andes,  but  its  body  consists 
mainly  of  sedimentary  deposits,  with  some  crystalline  rocks,  prob- 
ably ancient.  Both  have  suffered  from  severe  pressure  in  the  proc- 
ess of  mountain  making,  by  which  they  have  been  raised  not  unfre- 
quently  to  altitudes  of  thirteen  or  fourteen  thousand  feet.  Among 
them  deposits  of  various  ages,  from  the  Ordovician  to  the  Jurassic, 
have  been  identified,  so  that  probably  this  region  of  the  earth's  sur- 
face, or  at  any  rate  considerable  parts  of  it,  as  in  the  case  of  the 
Rocky  Mountains,  may  have  been  submerged  during  a  large  part  of 
the  Primary  and  Secondary  eras.  But,  so  far  as  we  know,  Tertiary 
deposits  do  not  form  an  important  element  in  the  constituents  of 
the  massif.  Ancient  volcanic  rocks  indicate  great  eruptions  long 
prior  to  that  era.  Elevated  plateaus  are  inclosed  between  the 
ranges,  and  from  lat.  5°  N.  to  40°  S.  the  watershed  generally  does 
not  fall  below  1 1,000  feet,  and  is  often  much  above  it.  Certain  huge 
spurs,  which  run  roughly  parallel  with  the  south  shore  of  the  Carib- 
bean Sea,  may  be  the  result  of  thrusts  connected  with  this  basin. 
The  courses  of  the  great  rivers  are  remarkably  simple.  The  head- 
waters of  the  Orinoco,  the  Amazon,  and  the  La  Plata  all  start  from 
the  flanks  of  the  Andes ;  the  first  and  second  run  eastward  on 
either  side  of  the  plateau  of  Guiana,  and  the  third  is  compelled  by 
the  vast  plateau  of  Brazil  to  take  a  course  almost  due  south.  Owing 
to  the  physical  structure  of  the  continent  already  mentioned,  the 
basin  of  the  Orinoco,  for  a  limited  distance,  is  separated  from  that 
Xof  the  Amazon  by  a  low  and  ill-defined  boundary,  and  the  same  is 
true  of  the  basin  of  the  latter  river  and  that  of  the  Rio  de  la  Plata. 
The  greater  part  of  the  coast  line  of  this  continent,  at  any  rate  south 
of  the  Orinoco  River,  resembles  that  of  Africa  in  its  regularity ;  but 
from  about  lat.  40°  S.  on  the  west  coast,  and  perhaps  as  much  as 
10°  further  north  on  the  east  coast,  the  abundance  of  islands  and 
fjords  indicates  that  the  whole  region  has  sunk  down  for  some 
hundreds  of  feet  at  a  date  geologically  recent. 

Such  an  admirable  outline  of  the  geology  of  Australia  is  given  by 
Mr.  Wallacef  that  I  venture  to  quote  his  account,  with  some  abbre- 
viation. We  may  conclude,  he  says,  "  that  the  eastern  and  the 
western  divisions  of  the  country  first  existed  as  separate  islands, 


*  Comparatively  few  of  these  are  still  in  activity, 
f  "  Island  Life,"  p.  464. 


428  TtiE  STORY  OF  OUR  PLANET. 

and  only  became  united  at  a  comparatively  recent  epoch.  This  is 
indicated  by  an  enormous  stretch  of  Cretaceous  and  Tertiary  forma- 
tions extending  from  the  Gulf  of  Carpentaria  completely  across  the 
continent  to  the  mouth  of  the  Murray  River.  During  the  Creta- 
ceous period,  and  probably  throughout  a  considerable  portion  of  the 
Tertiary  [era],  there  must  have  been  a  wide  arm  of  the  sea  occupy- 
ing this  area,  dividing  the  great  mass  of  land  on  the  west — the  true 
seat  and  origin  of  the  typical  Australian  flora — from  a  long  but  nar- 
row belt  of  land  on  the  east,  indicated  by  the  continuous  mass  of 
Secondary  and  Palaeozoic  formations  already  referred  to,  which 
extend  uninterruptedly  from  Tasmania  to  Cape  York."  As  no 
Tertiary  deposits  have  been  found  in  this  area,  it  may  have  extended 
from  north  to  south  without  a  break.  It  consists  of  a  basement  of 
ancient  crystalline  rocks,  supporting  Palaeozoic  and  Secondary  for- 
mations, the  latter  being  developed  on  both  sides  the  central  range, 
the  former  including  the  important  coal  fields  of  the  Newcastle  dis- 
trict, which  are  approximately  coeval  with  those  of  Britain.  So 
this  region  must  have  been  almost  submerged  in  the  Secondary  era. 
The  western  land  consists  of  a  large  mass  of  "  granite,  800  miles  in 
length  by  nearly  500  in  maximum  width,"  which  "  certainly  was 
once  buried  under  piles  of  stratified  rock,  and  then  formed  the 
nucleus  of  the  old  Western  Australian  continent." 

The  group  of  islands  constituting  New  ^Zealand  seems  to  have 
been  much  augmented  during  the  later  part  of  the  Tertiary  era. 
These  upward  movements  are  probably  connected  with  the  great 
outbursts  of  igneous  rock  *  which  characterize  several  localities. 
They  continued  to  a  very  late  date,  geologically  speaking,  though 
undoubtedly  the  physical  geography  of  the  southwestern  part  of 
the  Middle  Island  and  the  more  northern  part  of  the  North  Island 
point  to  still  later  movements  in  the  opposite  direction.  Speaking 
generally,  New  Zealand  exhibits  a  fairly  continuous  section  of  rocks 
belonging  to  the  three  geological  eras,  and  the  oldest  of  these  seems 
to  rest  upon  crystalline  rocks,  almost  certainly  Archaean  in  age. 
The  last  named  are  chiefly  exhibited  on  the  western  side  of  the 
islands.  Is  it  possible  that  here,  and  on  the  eastern  margin  of 
Australia,  we  find  the  last  fragment  of  a  very  ancient  mass  of  land 
now  fully  1 200  miles  apart?  The  intervening  sea  is  deep,  but  its 
bed  slopes  down  slowly  from  the  western  shore  of  New  Zealand,  so 


*  There  is  much  comparatively  modern  igneous  rock  in  Australia,  but  no  volcanoes  are 
still  active. 


THE  BUILDING  OF  EUROPE  AND  OTHER  CONTINENTS.       4*9 

that  an  area  far  broader  than  the  islands  is  included  within  the  thou- 
sand-fathom line,  from  which  one  long  spur  is  thrown  off  toward 
Queensland,  and  another  actually  links  on  to  the  north  of  Australia 
by  way  of  New  Caledonia. 

A  large  number  of  the  Oceanic  Islands  consists  either  of  volcanic 
rock  or  of  recent  calcareous  deposits,  commonly  connected  with 
coral  reefs.  But  in  a  certain  number  of  cases  not  only  those  of 
great  islands,  as  New  Zealand  and  Madagascar,  but  also  those  of 
smaller  size,  such  as  the  Chatham,  Tonga,  and  Marquesas  islands, 
New  Britain,  the  Fiji,  and  Solomon  archipelagoes,  etc.,  various 
deep-seated  igneous  rocks  or  clay  slates  and  old  sandstones  have 
been  observed.  Thus  the  general  rule  is  not  without  exceptions, 
and  in  other  cases  the  superficial  deposits  may  conceal  masses  of 
much  more  ancient  rocks.* 

*  As  remarked  by  Mr.  A.  Harker,  Geological  Magazine,  1891,  p.  252. 


CHAPTER  VI. 

A  SKETCH   OF  THE   EARTH'S  LIFE-HISTORY. 

THE  study  of  fossils  brings  before  our  eyes  the  fauna  and  flora  of 
the  globe  during  past  ages.  It  has  led  the  way  to  two  general 
conclusions :  the  one,  that  the  disappearance  of  any  group  of 
living  creatures  and  the  introduction  of  another  has  been  a  gradual 
process ;  the  other,  that  the  newer  types  are  related  more  or  less 
intimately  to  the  older.  The  first  conclusion  is  a  certainty;  not 
the  slightest  evidence  can  be  found  of  any  catastrophic  destruction, 
over  the  earth  as  a  whole,  of  its  living  tenants,  or  of  a  corresponding 
creation  of  a  number  of  new  species,  whether  of  plant  or  animal. 
The  second  conclusion  has  a  high  degree  of  probability ;  it  cannot 
as  yet  be  regarded  as  demonstrated,  but  the  arguments  against  it 
are  far  outweighed  by  those  in  its  favor. 

What  life  is  we  do  not  know ;  of  how  it  begins  we  are  equally 
ignorant.  When  the  curtain  draws  up  on  the  first  act  of  the  world's 
drama  of  life,  the  stage  is  already  occupied,  and  no  prologue 
speaker  comes  forward  to  narrate  the  events  which  have  led  up  to 
the  situation.  But  just  as  we  should  infer  from  the  opening  scene 
in  a  drama  preliminary  incidents  and  influential  motives  tending  to 
the  development  of  each  one  of  the  characters,  so  we  infer  from  a 
study  of  the  nature  and  structures  of  the  creatures  which  are  the 
first  discovered  that  they  were  preceded  by  others  and  were  in  some 
way  themselves  the  outcome  of  circumstance.  Legends  of  olden 
time  tell  of  people  who  sprang  from  the  earth  full  grown  and  nations 
which  were  autochthonous.  Science,  even  in  her  dreamland,  knows 
of  none  which  have  not  a  past  history  and  a  long  line  of  ancestors. 
Life  doubtless  had  a  beginning,  and  the  first  forms  were  probably  of 
an  embryonic  character ;  but  of  these  all  vestiges  have  been  com- 
pletely effaced. 

In  deciphering  the  record  of  the  rocks  we  find  that  the  story 
which  is  told  by  its  latest  lines  differs  little — if  at  all — from  the 
present  history.  For  instance,  in  the  coarse  flint  gravels  which  are 
found  at  various  elevations — commonly  less  than  a  hundred  feet 
— above  the  present  beds  of  rivers,  more  especially  in  the  south- 


A    SKETCH  OF    THE  EARTH'S  LIFE-HISTORY.  431 

eastern  half  of  England,  the  remains  of  a  few  creatures  now  extinct 
have  occurred.  When  all  the  land  on  the  site  of  London  between 
the  present  margin  of  the  Thames  and  the  line  of  the  Euston  Road 
was  washed  by  a  broader  and  more  rapid  river,  then  the  savage 
races  who  inhabited  its  banks  hunted  a  huge  elephant  and  a  rhi- 
noceros, both  of  which  have  since  disappeared  from  the  earth. 
In  that,  however,  there  is  nothing  strange.  Even  now  many  of  the 
larger  animals — those  which  are  either  more  profitable  or  more 
hostile  to  man — are  becoming  yearly  more  scarce.  The  wolf  has 
disappeared  from  Britain,*  the  lion  from  Greece  and  Syria,  the  hip- 
popotamus from  the  Lower  Nile  ;  the  bison,  the  fur  seal,  the  African 
elephant,  and  a  host  of  other  wild  animals  are  far  rarer  now  than 
they  were  in  the  last  century,  even  in  the  last  generation.  Within 
two  centuries  the  dodo,  the  solitaire,  the  great-auk,  Steller's  manatee, 
and  a  few  other  animals  have  become  actually  extinct,  vanishing 
before  the  face  of  man — a  destroyer  more  ruthless  than  any  wild 
beast,  for  it  slays  only  for  appetite,  he  for  greed  of  gain  or  lust  of 
slaughter,  both  insatiate.  The  older  any  extinct  type  is  proved  to 
be  the  less  closely  it  resembles  any  of  those  which  still  survive. 
Still  its  divergences  from  them  appear  to  be  in  accordance  with  some 
rule,  and  not  in  any  sense  spasmodic  and  eccentric.  Geology,  in 
fact,  demonstrates  the  actual  existence  in  a  remote  past  of  creatures 
not  less  strange  than  the  monsters  of  legends.  So  strong,  indeed, 
is  the  likeness  in  some  cases  that  one  could  fancy  that,  as  stories  of 
giants  sometimes  grew  out  of  discoveries  of  the  bones  of  mammoths 
or  other  large  mammals,  so  the  dragon  killed  by  St.  George,  or  the 
griffin  portrayed  by  the  Lombard  sculptor,  f  had  been  constructed 
by  some  prehistoric  Cuvier  or  Owen  from  relics  which  had  been 
actually  found.  But  until  a  remote  epoch  is  reached  geology  reveals 
nothing  widely  different  from  existing  forms,  and  it  never  exhibits 
anything  in  which  a  general  correspondence  with  some  known 
type  is  associated  with  some  bizarre  deviation.  It  finds  no  place 
for  the  Faun  or  the  Satyr,  the  Merman  or  the  Centaur,  the  Cyclops 
or  the  "men  whose  heads  do  grow  beneath  their  shoulders."  It 
unfolds— and  the  conviction  of  this  deepens  simultaneously  with  the 

*  The  last  wolf  is  said  to  have  been  destroyed  in  Scotland  in  1680,  and  it  lingered  about 
thirty  years  longer  in  Ireland  ;  the  reindeer  was  living  in  Caithness  in  1159,  ^he  brown 
bear  was  probably  destroyed  by  about  the  tenth  century,  the  beaver  disappeared  from 
Wales  shortly  after  the  twelfth  century,  and  the  wild  boar  became  extinct  before  the  reign 
of  Charles  I.—  Dawkins,  "  Cave  Hunting,"  ch.  iii. 

f  Ruskin,  "  Modern  Painters,"  part  iv.  ch.  vjii. 


432  THE   STORY  OF  OUR   PLANET. 

widening  of  knowledge — the  working  of  mighty  laws,  the  operation 
of  co-ordinated  forces.  Though  the  living  form  may  be  plastic  as 
clay  in  the  potter's  hands,  yet  in  Nature's  workshop  no  apprentices 
can  play  their  elf-like  tricks,  for  one  master  mind  directs  alike  in 
small  and  great. 

As  the  pedigree  of  life  is  followed  back  in  geological  history,  the 
ancestry  of  many  forms  now  living  can  be  distinctly  traced,  but  not 
a  few  are  found  which  appear  to  have  died  and  left  no  successors. 
It  is  also  made  evident  by  a  comparative  study  of  past  floras  and 
faunas  that  the  more  remote  they  are  from  the  present  time  the 
less  marked,  on  the  whole,  is  their  resemblance  to  living  types. 
Of  the  fauna  which  existed  in  the  later  part  of  the  Tertiary  era  the 
great  majority  still  survive,  of  the  earlier  one  comparatively  few. 
From  the  end  to  the  beginning  of  the  era  the  percentage  of  living 
forms  steadily  decreases,  while  that  of  extinct  correspondingly 
increases.  From  the  later  deposits  of  the  Secondary  hardly  a 
species — perhaps  not  a  single  one — has  survived.  During  that  era 
lost  genera  become  more  frequent,  then  families,  and  finally  even 
orders.  Still  everything  which  is  found,  even  in  the  earliest  strata, 
presents  some  resemblance  to  existing  types  of  life.  In  most  cases, 
if  not  all,  a  skilled  naturalist,  if  only  a  fairly  perfect  specimen  were 
placed  in  his  hands,  would  at  once  recognize  its  affinities  with 
some  of  the  orders  which  exist.  The  chief  difficulties  in  the 
classification  of  fossil  forms — apart  from  those  caused  by  the  nec- 
essary imperfection  of  the  materials* — arise  from  their  generalized 
character,  as  it  may  be  called.  They  differ  from  every  one  of  the 
existing  groups,  and  yet  present  structures  which  form  connecting 
links  with  several.  These  correspondences  also,  as  a  further  study 
indicates,  are  usually  of  a  more  or  less  embryonic  character ;  that  is 
to  say,  they  are  still  exhibited  by  life  forms  which  are  now  perfectly 
distinct,  but  this  is  only  in  the  earlier  stages  of  their  development ; 
the  resemblances  which  now  disappear  as  the  animal  becomes  adult 
were  then  stereotyped  and  became  characteristic  of  the  individual. 
To  put  the  matter  briefly  and  in  homely  phrase,  many  of  the  life 
forms  of  the  earliest  ages  were  merely  overgrown  babies. 

Nature,  as  we  have  said,  is  the  schoolmistress  of  all  living  crea- 
tures ;  and,  harder  than  the  sternest  of  all  human  pedagogues,  she 
never  spoils  the  child  by  sparing  the  rod  or  remits  the  penalty  for 

*  It  must  be  remembered  that  even  the  best  preserved  specimen  only  retains  the  hard 
parts  of  the  organism, 


A    SKETCH  OF    THE  EARTH'S  LIFE-HISTORY.  433 

any  crying.  The  motto  so  well  known  to  the  Wykehamist  seems  to 
be  writ  large  on  the  walls  of  her  schoolhouse  :  "  Aut  disce,  aut  dis- 
cede,  manet  sors  tertia  caedi,"  which  may  be  thus  freely  Englished  : 
"  Change  yourself  as  conditions  change  ;  begone  elsewhere  would 
you  live  as  you  did,  or  stay  to  suffer  and  to  die."  The  choice  is 
often  only  between  the  first  and  the  last — the  ill-fated  creature  is 
sometimes  caught  in  the  proverbial  position  between  the  fiend  and 
the  deep  sea — for  instance,  to  a  shore  crab  the  one  is  represented  by 
the  rising  land,  the  other  may  be  an  actuality.  So  it  must  become 
a  land  crab  or  an  extinct  species ;  but,  even  where  it  has  been  able 
to  migrate,  the  movement  and  the  inevitable  changes  in  condition,* 
though  slight,  produce  their  effects,  and  some  variation  is  generally 
the  result.  The  appearance  of  a  new  fauna  or  flora  is  indicative  of 
a  period  of  change.  "  Quieta  non  movere  "  may  be  taken  as  the 
motto  of  a  species  ;  yielding  place  is  one  of  the  results  of  specializa- 
tion. 

Earth's  children  are  put  at  once  to  school ;  Nature  is  its  mistress, 
and,  though  she  takes  her  scholars  from  the  breast,  does  not  adopt 
the  methods  of  the  kindergartens.  All  creatures,  by  the  discipline 
of  life,  by  the  endless  influences  of  a  changing  environment,  have 
been  gradually  developed,  specialized,  and  molded  till  they  have 
come  nearer  to  the  forms  which  at  present  exist.  Organisms,  like 
men,  have  a  pedigree  ;  even  with  our  imperfect  knowledge  a  family 
tree  in  most  cases  can  be  constructed  for  each  particular  group. 
This,  no  doubt,  did  we  know  the  whole  history,  could  be  expanded 
so  as  to  unite  all  living  things  and  cover  all  time  ;  then  the  analogy 
between  the  trees,  genealogical  and  botanical,  would  be  complete. 
As  the  latter  rises  from  the  soil  under  which  its  roots  are  concealed, 
none  the  less  real  because  they  are  unseen,  so  the  former  would 
appear  at  the  first  epoch  of  geological  history,  supported  in  reality 
on  an  unknown  and  irrecoverable  ancestry.  As  the  central  stem 
rises  from  the  ground,  it  throws  off,  first  one  branch,  then  another ; 
some  of  these  evidently  were  never  healthy  growths,  and  speedily 
withered  away ;  others,  though  they  prospered  for  a  time,  have 
ceased  to  increase,  and  now  are  dwindling,  if  not  actually  dead  ; 
while  others  are  still  in  full  vigor,  year  by  year  putting  forth  leaf 
and  flower,  twig  and  fruit. 

Among  mankind  the  annals  of  a  family  are  a  history  of  failures 
and  successes.  This  branch  has  gone  to  the  bad,  that  has  prospered 

*  Since  probably  hardly  any  two  places  in  the  world  are  exactly  alike. 


434  THE    STORY  OF  OUR   PLANET. 

exceedingly.  So  it  has  been  in  nature.  Her  chronicle  of  life  is 
full  of  examples  of  either  fate.  It  is  suggestive  of  endless  analogies 
with  the  varied  stories  of  human  life,  with  the  ups  and  downs  of 
individuals  and  nations.  Perhaps  some  day,  when  we  know  more, 
we  may  say  more  boldly  than  now  "  which  things  are  an  allegory," 
and  perceive  more  clearly  that  in  every  phase  of  life's  history,  from 
•the  lowest  to  the  highest,  "through  the  ages  an  increasing  purpose 
runs."  In  the  narrow  round  of  each  man's  life  the  memories  evoked 
by  turning  over  the  portraits  in  an  old  photograph  album  are  apt 
to  be  sad.  There  are  so  many  who  have  failed  in  life,  or  have  died 
young.  Of  such  records  the  stone  pages  of  nature's  picture-book 
are  full.  Again  and  again  we  come  across  the  remains  of  some  type 
which  obviously  never  was  a  success.  Why  and  wherefore  we  are 
not  told,  but  the  fact  is  certain.  The  genera  are  few,  and  no  one 
of  them  was  ever  represented  by  many  species.  The  type  was  never 
numerous,  even  individually.  For  whatever  time  it  may  have  strug- 
gled on — and  the  period,  geologically  speaking,  usually  is  not  very 
long — its  members,  like  the  conies,  were  always  a  feeble  folk.  Like 
some  families  am«ng  ourselves,  they  never  make  much  mark  in  the 
world,  and  are  not  even  prolific  of  paupers.  A  different  fate 
attends  another  series  of  living  creatures  ;  these  are  never  numer- 
ous, but  they  are  extremely  persistent ;  they  are  represented  age 
after  age  by  a  limited  number  of  species,  and  but  seldom  are  indi- 
vidually abundant ;  they  are  apparently  not  very  flexible,  but  they 
are  strongly  enduring.  They  resemble  some  of  the  "  statesmen " 
and  "dalesmen  "of  our  northern  agricultural  districts,  at  any  rate 
before  the  general  upset  of  the  last  half  century,  when  son  suc- 
ceeded father  for  almost  untold  generations,  and  the  changeful 
influence  of  the  outer  world  penetrated  but  slowly.  Most  people 
know  the  pearly  nautilus ;  *  it  is  not  a  very  abundant  "  shell "  at  the 
present  day.  The  genus  in  the  past  was  always  represented  by  a 
few  species,  and  none  of.  these  ever  swarmed  in  the  sea,  yet  it  may 
be  traced  back  well  into  Palaeozoic  times.  A  creature  with  a  bivalve 
shell,  called  Lingula,  one  of  the  living  brachiopods,  has  a  yet  longer 
history,  for  it  actually  goes  back  into  the  Ordovician  ;  and  if  a 
closely  allied  form  (Lingulclld)  be  included,  as  it  was  formerly,  in 
the  genus,  it  is  one  of  the  very  earliest  fossils  which  have  yet  been 
discovered  in  the  Cambrian  strata. 

By  other  types  of  life  an  extraordinary  fecundity  and  variability 

*  Nautilus pompilius ,  living  in  the  Pacific,  near  the  Moluccas,  Fiji,  and  adjacent  islands. 


A    SKETCH  OF    THE   EARTH'S  LIFE-HISTORY. 


435 


are  exhibited.  They  were  apparently  very  sensitive  to  external 
stimulus,  and  prompt  to  modify  themselves  accordingly.  Thus  the 
number  of  representative  species  is  large,  and  the  individual  communi- 
ties are  numerous,  but  each  species  lasts  for  a  comparatively  short 
time.  No  better  examples  of  them  can  be  found  than  in  the  genus 
Ammonites,  as  formerly  defined.*  These  creatures  belong,  like  the 
nautilus,  to  the  Cephalopods.  Their 
shell  also  is  chambered  and  coiled 
in  a  plane  spiral  with  the  whorls  in 
contact,  and  the  chambers  are  con- 
nected by  a  sort  of  pipe,  or  "  siph- 
uncle."  This  is  dorsal  in  position — 
that  is,  placed  against  the  outer 
"  keel  "  of  the  shell — and  the  su- 
tures, or  lines,  where  the  "  septa," 
dividing  the  chambers,  meet  the 
shell,  assume  very  complicated 
forms,  somewhat,  leaf-like  in  outline. 
These  are  the  most  obvious  points 
of  difference  from  the  nautilus  ;  but 
their  history  in  many  respects  is 

curiously  diverse  from  that  of  this  genus.  In  Northwestern  Europe 
they  make  their  appearance  in  the  Trias,  but  the  occurrence  of  a  kin- 
dred and  rather  more  simplified  form  indicates  that  even  then  the 
process  of  specialization  was  not  quite  complete,  while  forerunners  of 
a  more  generalized  character  are  found  in  the  later  members  of  the 
Primary  series.  Toward  the  end  of  the  Trias  the  genus  had  got  a 
firm  footing,  and  it  lasts  all  through  the  Secondary  era.  The  number 
of  species  is  very  great,  but  their  duration  is  frequently  so  limited 
(though  their  geographical  range  is  wide)  that  no  form  of  life  is 
found  more  useful  than  the  Ammonite  for  subdividing  a  group  or 
a  stage  into  zones.  All  through  the  Jurassic  system  the  "  zone  of 
Ammonites  so-and-so  "  is  employed  almost  as  confidently  as  a  con- 
sulship or  archonship  in  classic  history.  After  this  period  the 
endeavor  to  adapt  themselves  to  circumstances  seems  to  become 
yet  more  marked.  In  Triassic  and  Jurassic  times  the  family  rarely 
departs  from  the  "  plane  spiral  "  as  its  fundamental  type  of  growth. 
But  instances  of  deviation  become  commoner  in  the  Neocomian, 
and  frequent  in  the  Cretaceous.  Always  there  is  a  long  row  of 


FIG.  145.— SEPTUM  AND  SUTURES  OF 
(a)  AMMONITES,  (&)  CERATITES 
(FROM  THE  TRIAS),  (e)  NAUTILUS. 


*  The  genus  is  now  split  up  into  several  genera. 


436  THE   STORY  OF  OUR  PLANET. 

chambers,  increasing  gradually  in  size,  but  this  may  be  straight  as  a 
ruler,  hooked  like  a  walking  stick,  bent  up  into  a  plane  or  a  helicoid 
spiral,  the  whorls  being  in  contact,  or  separate,  or  arranged  in  some 
more  complex  pattern,  intermediate  between  or  combining  certain 
of  these.  Then  the  family  disappears.  May  it  be  compared  to 
certain  firms  with  a  long  and  prosperous  history,  which  have  plunged, 
when  the  tide  seemed  to  be  turning  against  them,  into  reckless 
speculations,  with  bankruptcy  as  the  final  end?  It  is  clear  that  no 
life  form  can  maintain  itself  in  the  struggle  for  existence  unless  it 
possesses  sufficient  pliability  to  respond  to  changes  in  its  environ- 
ment ;  but  appearances  sometimes  suggest  that  this  may  be  carried 
too  far,  and  the  end  precipitated  by  a  premature  exhaustion  of  vital- 
ity caused  by  the  desperate  efforts  to  escape  the  impending  doom. 
At  any  rate,  it  seems  certain  that  highly  specialized  forms  are  the 
more  sensitive  to  external  stimulus ;  hence  they  have  the  shortest 
duration  in  time,  because  they  are  either  changed  by  evolutionary 
process,  or  else  are  brought  to  an  untimely  end.  The  latter  fate  is 
by  no  means  uncommon  ;  for  the  effects  of  any  disturbance  of  the 
balance  obviously  may  be  more  serious  in  a  complex  organism  than 
in  one  of  simpler  structure.  Forms  of  a  low  organization  have  an 
enormous  persistency.*  They  are  probably  insensible  to  slight 
changes,  and  readily  find,  if  forced  to  migrate,  conditions  suitable 
for  their  existence.  But  even  in  the  cases  where  an  organism  is 
being  modified  it  does  not  follow  that  any  record  of  this  will  remain. 
In  a  time  of  active  physical  change  denudation  may  alternate  with 
deposition.  Even  when  the  change  is  brought  about  by  a  gradual 
subsidence,  the  development  of  one  species  from  another  may  be 
difficult  to  follow.  A  new  fauna  seems  more  commonly  to  arrive 
like  colonists,  the  older  one  migrating  or  becoming  extinct  before 
the  invader.  The  new  form  may  have  been  actually  developed 
under  conditions  which  were  less  favorable  to  the  preservation  of  a 
record.  The  epoch  of  a  nation's  birth  is  not  generally  the  most 
complete  in  its  history.  We  know  more  of  the  decline  of  the  Roman 
Empire  than  of  the  rise  of  the  races  from  which  modern  Europe 
grew  up. 

But  among  all  these  changes  one  thing  is  noteworthy — there  is 
no  repetition.  When  once  a  type  has  become  extjnct,  it  is  never 
reproduced  either  in  the  same  or  in  any  other  part  of  the  globe.  It 

*  Foraminifera,  for  instance,  have  continued  through  several  geological  periods  without 
any  apparent  change ;  but  these  creatures  are  so  variable  that  it  is  difficult  to  say  what 
defines  a  species  among  them. 


A    SKETCH  OF   THE  EARTH'S  LIFE-HISTORY.  437 

is  this  which  makes  a  classification  by  organic  remains  possible. 
"  The  order  of  succession  established  in  one  locality  holds  good 
approximately  in  all."*  Another  thing  also  may  be  noted.  In 
Nature  the  saying  "  Ilka  dog  has  its  day  "  seems  often  to  hold  good. 
A  particular  order  or  family  increases  largely,  and  exhibits  great 
powers  of  variation,  after  which  it  dwindles  or  disappears,  when 
something  else  seems  to  take  its  place.  For  instance,  the  corals  of 
the  Palaeozoic  era  differ  so  greatly  in  structure  from  those  now  living 
that  a  large  number  of  them  have  been  put  into  a  different  order. 
Again,  there  were  times  when  among  "  bivalve  shells  "  brachiopods 
swarmed  and  lamellibranchs  were  rare  ;  the  contrary  is  now  the  case. 
The  trilobites  had  made  their  appearance  at  the  dawn  of  geological 
history ;  afterward  they  increased  and  multiplied  greatly,  and  then 
utterly  disappeared.  These  instances  may  suffice  ;  the  list  could  be 
readily  augmented. 

Again,  the  great  divisions  of  organic  life  seem  to  be  affected  in 
turn  by  tendencies  to  change.  Each  passes  through  an  epoch  of 
marked  development,  and  then  becomes  comparatively  stationary. 
It  appears  to  lose  its  power  of  adaptation  to  circumstances;  it 
becomes  a  palaeontological  Spain  or  Turkey.  In  such  case  it  very 
often  dwindles  and  vanishes  from  the  scene,  for  in  the  animal  world 
a  nation  is  not  kept  in  existence  by  the  mutual  jealousies  of  its 
stronger  neighbors.  But  even  where  the  vitality  of  a  race  is  not 
exhausted,  it  appears  to  reach  after  .a  time  the  limits  of  variation, 
at  any  rate  in  the  more  important  matters,  and  subsequent  changes 
are  specific  rather  than  generic.  Possibly  certain  types  of  the  order 
or  class  have  been  produced  which  are  fairly  well  adapted  to  the 
conditions  of  life  dominant  on  the  globe,  and  are  thus  able  to  remain 
until  the  vitality  of  the  several  species  is  exhausted ;  for  in  the 
biological,  no  less  than  in  the  physical,  world  the  law  of  dissipation 
of  energy  seems  to  hold,  and  the  race  at  last  to  die,  as  the  individual 
may  die,  of  sheer  old  age. 

We  cannot  attempt  in  this  volume  more  than  a  brief  sketch  of  the 
succession  of  life  on  the  globe,  for  any  full  description  would  require 
the  introduction  of  too  many  technicalities.  Beginning  with  plants, 
we  must  remember  that  a  fossil  flora  is  likely  to  be  a  very  imperfect 
representative  of  the  flora  of  any  region.  It  will  indicate  the  vegeta- 
tion of  the  sea,  the  lake,  the  stream,  the  marsh,  or  the  lowland 
generally ;  that  of  the  upland  and  the  mountain  will  be  rarely  pre- 

*  Huxley,  Address  to  Geological  Society,  1870.     ("  Lay  Sermons  and  Addresses,"  X.) 


438  THE   STORY  OF  OUR  PLANET. 

served.  The  botanical  record  is  probably  even  more  fragmentary 
than  the  zoological.  Plants  naturally  might  be  expected  to  have 
come  into  existence  at  least  as  early  as  animals.  A  consistent  evolu- 
tionist would  hope  to  find  the  germ  of  the  subsequent  "tree  of  life  " 
in  some  embryonic  form,  which  was  neither  plant  nor  animal,  but 
was  so  destitute  of  definite  structures  that  it  could  not  be  assigned 
with  confidence  to  either.  Of  any  such  embryonic  form  we  know 
nothing ;  moreover,  plant  remains  that  are  beyond  all  suspicion  are 
not  found  until  we  have  passed  through  several  chapters  of  the 
earth's  history.  In  the  Cambrian,  it  is  true,  numerous  objects 
occur  which  have  been  called  fucoids,  because  they  were  supposed 
to  be  seaweeds,  and  have  received  generic  and  specific  names,  but 
in  no  case  is  the  identification  with  plants  at  all  certain.  It  is  just 
possible  that  some  may  be  very  imperfectly  preserved  stems  or 
leaves,  but  the  majority,  more  probably,  are  either  inorganic  struc- 
tures, such  as  may  be  produced  by  running  water,  the  filling  up  of 
shrinkage  cracks  and  the  like,  or  tracks  which  have  been  made  by 
worms  and  other  crawling  creatures.  Passing  by  these  doubtful 
"  seaweeds  " — the  only  evidence  in  favor  of  the  existence  of  plants 
in  the  whole  of  the  Cambrian  period — the  first  indubitable  plant 
occurs  in  the  Skiddaw  (Arenig)  rocks  of  Cumberland,  and  so  was 
living  at  the  beginning  of.  the  Ordovician.  The  genus  is  named 
Buthotrepkis,  and  two  species  are  supposed  to  occur.  Its  affinities 
are  doubtful.  Some  think  it  an  alga,  others  a  rhizocarp,  and  a  dis- 
tant connection  of  the  living  Pillwort  (Pilularia).  The  Ordovician 
system  has  furnished  two  or  three  other  plant  remains  of  uncertain 
botanical  position,  and  even  the  Silurian  has  not  proved  to  be  very 
much  richer.*  In  it  rhizocarps  are  again  found,  but  two  of  its 
plants  must  have  attained  to  a  considerable  size.  The  botanical 
position  of  one  called  NcmatopJiyton  is  doubtful ;  some  consider  it 
to  be  a  huge  seaweed  ;  others,  a  conifer,  or,  at  any  rate,  one  of  the 
gymnosperms.  The  remaining  plant  is  regarded  as  a  relative  of 
the  club-mosses  (Lycopodiacece}.  These,  however,  are  now  lowly 
plants  ;  this  one  was  a  tree. 

In  the  Devonian  system  vegetable  remains  become  much  more 
abundant.  In  this  country  they  are  still  comparatively  rare,  but 
a  considerable  flora  has  been  recovered  from  various  districts  in 
Eastern  North  America — e.  g.,  from  the  neighborhood  of  Cape 

*  One  of  the  most  interesting  discoveries  was  in  the  neighborhood  of  Corwen,  by  Ur. 
H.  Hicks,  about  on  the  level  of  the  base  of  the  Wenlock  group,  or  possibly  the  top  of 
the  Upper  Llandovery. 


A    SKETCH  OF   THE  EARTH'S  LIFE-HISTORY. 


439 


Gaspe  and  Southern  New  Brunswick,  in  Canada,  and  from  localities 
in  New  York,  Pennsylvania,  and  Ohio.  More  than  a  hundred 
species,  belonging  to  about  ninety-five  genera,  have  been  de- 
scribed.* The  vegetation  of  this  period  was  closely  related  to 
that  of  the  Carboniferous,  so  that  in  any  general 
statement  the  two  may  be  coupled  together.  The 
flora  of  the  latter  is  a  remarkably  rich  though  a 
very  singular  one.  Europe  alone  has  afforded 
176  genera  and  1370  species,  and  in  Great  Britain 
plant  remains  have  been  furnished  by  all  the  great 
subdivisions  of  the  system  from  the  bottom  to 
the  top  ;  but  here,  as  in  other  countries,  the  flora 
of  the  older  parts  is  less  rich  than  that  of  the 
newer.  The  vegetation  is  peculiar.  Much  uncer- 
tainty still  prevails  upon  several  points,  largely 
clue  to  the  imperfect  preservation  of  the  remains 
and  to  the  difficulties  in  bringing  the  plants  into 
line  with  existing  divisions,  but  the  following 
general  statements  represent  the  present  stage  of 
knowledge.  Ferns,  often  tree-ferns,  were  abund- 
ant. Besides  these,  tall  branchless  stems,  "exhib- 
iting in  habit  of  growth  and  fructification  a  close 
resemblance  to  our  modern  equisetum "  f  or  horsetails,  formed 
"dense  thickets,  like  southern  cane-brakes."  These  plants  (Cal- 
amites)  far  outgrew  their  modern  allies, 
attaining  a  height  of  some  thirty  feet. 
Not  less  common  were  a  number  of 
tree-like  plants  (Lepidodendron^  Sigilla- 
ria),  which  appear  to  have  been  most 
nearly  allied  to  the  club-mosses  (Lyco- 
podium),  but  which  occasionally  rose 
forty  feet  above  the  ground.  Spores 
and  spore-cases,  referred  to  these  plants, 
are  often  abundant,  and  sometimes 
make  up  whole  layers  of  coal.  Similar 
plants  are  found  in  the  Devonian  rocks. 
The  modern  conifers  were  represented 
by  a  genus  Cordaites  and  other  plants, 


FIG.  146. 

CALAMITES 

CANN/EFORMIS. 


FIG.  147. 
LEPIDODENDRON  ELEGANS. 


*  Sir  W.  Dawson,  "  The  Geological  History  of  Plants,"  ch.  iii.  (International  Scientific 
Series). 

f  Dawson,  "  The  Geological  History  of  Plants,"  ch.  iv. 


440  THE   STORY  OF  OUR  PLANET. 

which  appear,  on  the  whole,  to  be  most  closely  allied  to  some  of 
the  broader  leafed  yews,  such,  for  instance,  as  the  Salisburia  or 
gingko  tree  of  China  ;  but  these  were  less  abundant  than  the  forms 
already  named,  at  any  rate,  in  the  swamps  of  the  Carboniferous 
period ;  for  of  the  vegetation  of  its  highlands,  as  already  said, 
we  know  so  little  that  we  may  readily  form  a  very  incorrect  idea  of 
the  vegetation  of  the  earth  as  a  whole. 

The  Permian  rocks  are  not  very  rich  in  fossil  plants,  but  the  vege- 
tation as  a  whole  is  related  to  that  of  the  Coal  Measures,  though 
the  latter  obviously  is  beginning  to  give 
place  to  forms  of  more  modern  character 
and  higher  development.  By  the  begin- 
ning of  the  Secondary  era  the  change  had 
become  very  marked.  Here  the  "  old 
Carboniferous  forms  of  plants  finally  pass 
away,  to  be  replaced  by  a  flora  scarcely 
more  advanced,  though  different,  and 
consisting  of  pines,  cycads,  and  ferns, 
with  gigantic  equiseta,  which  are  the 
successors  of  the  genus  Catamites,  a  genus 
which  still  survives  in  the  Early  Trias.  .  . 
FlG  I48  The  cycads  are  a  new  introduction.  The 

SIGILLARIA  L^VIGATA.  whole,   however,    come   within    the    lim- 

its of  the    cryptogams  and    the   gymno- 

sperms,  so  that  here  we  have  no  advance.  As  we  ascend,  how- 
ever, in  the  Secondary  we  find  new  and  higher  types.  Even 
within  the  Jurassic  epoch,  the  next  in  succession  to  the  Trias,  there 
are  clear  indications  of  the  presence  of  the  endogens,  in  species 
allied  to  the  screw-pines  and  grasses  ;  and  the  palms  appear  a  little 
later,  while  a  few  exogenous  trees  have  left  their  remains  in  the 
Neocomian  ;  and  in  the  Cretaceous  these  higher  plants  come  in 
abundantly  and  in  generic  forms  still  extant,  so  that  the  dawn  of 
the  modern  flora  belongs  to  the  Cretaceous."  *  According  to  Sir 
W.  Dawson  only  twenty  species  of  Dicotyledons  have  been  dis- 
covered in  the  Neocomian.  In  the  lower  part  of  the  Cretaceous 
(including  the  equivalents  of  the  Gault,  Upper  Greensand,  and 
Chalk  Marl  of  this  country)  the  number  rises  to  357.  "Thus  we 
have  a  great  and  sudden  inswarming  of  the  higher  plants  of  modern 
types  at  the  close  of  the  Neocomian."  From  that  period  the  vege- 

*  Dawson,  "  Geological  History  of  Plants,"  ch.  v. 


A    SKETCH  OF   THE  EARTH'S  LIFE-HISTORY.  441 

tation,  the  remains  of  which  are  often  abundant,  gradually  draws 
nearer  to  that  which  still  exists,  indicating  the  same  distribution 
into  zones  related  to  temperature  as  at  present,  but  bearing  testi- 
mony to  very  remarkable  mutations  of  climate,  to  which  reference 
will  be  made  in  a  later  chapter.  For  the  present  it  may  suffice  to 
say  that  this  flora  indicates  a  gradual  change  from  a  climate  not 
very  different  from  that  which  at  present  prevails  in  the  neighbor- 
hood of  London  to  one  in  the  Middle  Eocene,  when  it  was  more 
like  that  now  characteristic  of  Northern  Africa.  This  was  followed 
by  a  gradual  refrigeration,  until  a  considerable  part  of  Britain  was 
buried  beneath  snow  and  ice  and  the  vegetation  of  the  remainder 
was  distinctly  arctic  in  character.  From  this,  the  so-called  Glacial 
epoch,  the  climate  has  gradually  improved  up  to  the  present  time. 

Thus  the  botanical  history  of  the  earth  comprises  three  great 
eras,  which,  however,  are  not  separated  by  any  hard  and  fast  lines ; 
the  first  characterized  by  ferns  and  gigantic  lycopods  and  horsetails; 
the  second,  in  which  cycads,  conifers,  and  palms  predominated  ;  and 
the  third,  when  the  larger  plants,  as  at  the  present  time,  were  mostly 
dicotyledons ;  and  this  class,  as  a  whole,  was  the  most  numerous. 
These  great  life-groups  of  plants,  it  should  be  noticed,  are  not  in 
any  chronological  relation  with  the  principal  steps  in  the  develop- 
ment of  animal  life. 

This,  as  has  been  already  said,  did  not  actually  begin  with  the 
Cambrian  period,  but  any  earlier  remains  are  ill-preserved  and 
rather  uncertain  in  character.  But  low  down  in  the  oldest  strata  of 
that  system — the  Harlech  group — fossils  occur  which  can  be' identi- 
fied with  certainty,  and  these  represent  more  than  one  class  of  the 
animal  kingdom.  The  strata  at  St.  David's  have  been  more  prolific 
than  any  other  in  the  British  Isles,  though  even  there  fossils  are 
very  far  from  abundant.  Sponges,  worms,  crustaceans,  brachio- 
pods,  and  pteropods  occur — in  all,  over  thirty  species.  The  Crustacea 
are  represented  by  some  creatures  of  small  size,  distantly  related  to 
the  existing  "  water-fleas,"  and  by  trilobites.  The  latter  is  an 
extinct  order,  resembling  in  some  respects  the  living  king-crabs 
(Limulus),  in  others  the  members  of  the  order  Isopoda,  to  which  the 
familiar  woodlouse  belongs.  The  body  consisted  of  a  series  of 
segments,  varying  in  number  from  two  to  twenty,  with  a  solid  tail 
and  with  a  head  formed  of  three  pieces,  more  or  less  firmly  fastened 
together,  the  whole  being  divided  into  three  lobes,  from  which 
characteristic  the  name  is  taken.  On  the  under  side  were  about 
eight  pairs  of  slender  legs.  A  trilobite  is  commonly  from  about  six 


442 


THE   STORY  OF  OUR  PLANET. 


FIG.  149. 
RESTORATION  OF  OLENELLUS. 


lines  to  a  couple  of  inches  long  ;  some  species,  however,  are  very 
minute,  while  others  exceed  a  foot  in  length.  Curiously  enough,  a 
species  of  the  largest  known  trilobite  (Paradoxides — Fig.  132) 
and  of  the  smallest  (Agnostus)  occur  side  by  side  in  the  Harlech 
group;  but  the  oldest  genus  which 
hitherto  has  been  detected,  and  now 
serves  to  indicate  the  lowest  zone  in 
the  Cambrian  system,  is  named  Olen- 
ellus  (Fig.  149).  This  as  yet  has  not 
been  discovered  at  St.  David's,  but  it 
has  been  found  in  Shropshire  and  in  the 
Northwest  Highlands,  as  well  as  in 
several  localities  out  of  England.  The 
genus  Paradoxides  ranges  through  the 
remainder  of  the  Harlech  and  the  Men- 
evian,  and  is  succeeded  by  Olenus  in 
the  Lingula  Flags.  Though  the  fauna 
of  the  Harlech  group,  comparatively 
speaking,  is  a  poor  one,  the  dawn  of 
life  cannot  have  been  very  recent,  for 
too  many  classes  are  represented,  and 
too  high  a  stage  of  development  has  been  reached. 

Henceforth  the  fauna  increases  in  number  and  variety,  though,  of 
course,  a  page  may  occur  here  and  there  in  the  record  which  is 
either  a  blank  or  nearly  so  ;  at  any  rate,  in  particular  localities.  The 
Menevian  fauna  runs  up  to  fifty-two  species,  of  which  more  than 
one-half  are  trilobites.  A  new  class — the  echinodermata — is  repre- 
sented by  a  cystidean.*  The  Lingula  Flags  are  frequently  rich  in 
individuals.  For  instance,  slabs  of  the  rock  are  often  thickly  spotted 
with  the  remains  of  the  little  brachiopod  (Lingulella  davisit)  from 
which  the  group  was  named  ;f  but  the  number  of  species  is  not 
materially  altered.  A  new  class  is  represented  by  the  net-like  fossil 
Dictyonema,  but  whether  this  be  a  hydrozoan  or  a  polyzoan  is  not 
quite  certain.  The  opinion  of  experts  now  inclines  to  the  former 
view.  A  new  order  of  the  Crustacea,  the  Phyllopoda,  is  represented. 
In  the  Tremadoc  group  the  number  of  species  increases  to  eighty- 
six.  The  orders  already  mentioned  are  represented,  but,  in  addi- 

*  The  Cystidea  are  an  order  bearing  some  likeness  to  the  living  Crinoids  (sea-lilies)  and 
Echinids  (sea-urchins).  They  were  never  very  abundant,  and  became  extinct  in  the  Car- 
boniferous period. 

fit  was  then  considered  to  be  a  true  Lingula. 


A    SKETCH  OF   THE  EARTH'S  LIFE-HISTORY. 


443 


tion,  more  than  one  new  form  of  importance  appears.  Among  the 
Hydrozoa  two  genera  occur  as  the  forerunners  of  the  graptolites,  an 
order  which  becomes  of  great  importance  in  Ordovician  times. 
Among  the  echinoderms  the  first  "sea-lily"  (Dendrocritius)  and 
the  first  "  starfish  "  (Palceasterind)  appear,  and  the  lower  parts  -of 
the  Tremadoc  have  furnished  the  first  heteropod,  a  "  univalve,"  and 
the  first  lamellibranch  or  ordinary  bivalve  mollusk.  The  former 
class  is  represented  by  the  genus  Bellerophon,  the  latter  by  no  less 
than  five  genera  and  twelve  species,  many  of  them  belonging  to  the 
existing  family  of  the  Arcadce  or  ark-shells.  Here  also  are  the  first 
cephalopods.  Two  genera  have  been  found,  one  of  which  (Ortho- 
ceras]  survived  even  into  Secondary  times. 

As  already  stated,  the  Tremadoc  group  has  been  included  by 
some  writers  with  the  Ordovician,  but  it  is  by  no  means  clear  that 
the  change  is  an  improvement.  According  to  Mr.  R.  Etheridge 
"  no  less  than  forty  genera  make  their  first  appearance  in  the  Arenig 
rocks  in  the  British  Islands."  At  the  time  when  he  wrote  (i  88  1) 
the  total  fauna  of  the  group  comprised  150  species.  Of  these  only 
sixteen  have  come  up  from  the  Tremadoc  group,  and  nine  pass  up 
into  the  overlying  Llandeilo  group.  It  is  therefore  curiously  dis- 
tinct as  a  fauna;  and  so  far  as  percentage  of  species  goes,  the 
Tremadoc  group  is  a  little  more  closely  attached  to  it  than  it  is  to 
the  overlying  Llandeilo  ;  nevertheless  the  marked  change  exhibited 
by  the  Arenig  fauna  and  the  incoming  of 
forms  abundant  throughout  the  Ordo- 
vician  indicate  that  much  may  be  said  in 
favor  of  the  earlier  arrangement.  The 
most  remarkable  feature  in  the  Arenig 
fauna  is  the  abundance  of  graptolites, 
which  formerly  were  supposed  not  to 
occur  in  any  earlier  deposits.  This,  as 
stated  above,  is  now  known  to  be  an  incor- 
rect view,  but,  after  all,  only  the  pre- 
cursors of  the  order  arrived  in  the  later 
part  of  the  Tremadoc.  The  graptolites 
form  an  extinct  order  of  the  Hydrozoa, 
which  had  a  certain  resemblance  to 

the    living    sertularians,     represented    by 
.1  r-      „  ,1       TJ  ...  , 

the       sea-firs      common     on    the   British 

coasts.  The  solid  part  (see  Fig.  150)  consisted  of  a  chitinous 
material,  and  formed  a  hollow  tube  (fr),  strengthened  by  a 


FlG-  150.—  STRUCTURE  OF 
A  GRAPTOLITE. 


444 


THE   STORY  OF  OUR  PLANET. 


rod  or  axis  (c  d},  and  communicating  with  a  series  of  cups  (a  a),  in 
which  the  individual  polyps  were  lodged.  Both  single  and  branched 
forms  occur,  exhibiting  considerable  variety,  and  the  cups  are  some- 
times arranged  on  one  side  of  the  axis,  sometimes  on  both,  the 
latter  being  almost  restricted  to  the  Ordovician  rocks,  in  which  also 
a  form  occurs  having  four  rows  of  cups  set  crosswise.  Graptolites 
are  supposed  to  have  traveled  to  this  country  from  America,  as  the 
number  of  genera  and  species  is  larger  there,  while  it  is  smaller  in 
Scandinavia  and  in  Bohemia  than  in  Britain.  Trilobites  continue  to 
increase  in  number,  and  genera  now  make  their  appearance  which 
have  a  long  range  in  time.  Brachiopods  become  more  numerous, 
but  the  lamellibranchs  are  still  very  few.  Gasteropods,  however,  or 
ordinary  univalve  mollusks,  are  now  first  found,  four  species  being 
known  ;  two  of  them  belonging  to  the  genera  Euomphalus  and 
Pleurotomaria,  which  afterward  become  rather  common,  and  last  for 
a  long  time. 

In  the  Llandeilo  group  corals  first  appear.  They  are  represented 
by  three  genera  *  and  as  many  species,  one  of  them  being  the 

familiar  chain  coral  (Halysites 
catemilatus).  Graptolites  are  plen- 
tiful, but  the  echinoderms  are  as 
yet  very  scanty.  Brachiopods  are 
becoming  more  numerous,  for 
thirty-four  species  are  found,  but 
the  mollusks  are  still  only  slightly 
represented.  The  whole  Llan- 
deilo fauna  consists  of  175  species, 

and  forty-seven  of  the  genera  are 
FIG.  151.— HALY  SITES  CATENULATUS. 

new. 

The  Caradoc  or  Bala  fauna  is  a  rich  one,  numbering  614  species, 
the  classes  most  strongly  represented  being  the  Crustacea  (146 
species)  and  the  BVachiopoda  (109  species).  The  former  are  mostly 
trilobites,  this  order  now  attaining  its  maximum.  There  is  a  marked 

*  The  older  classification  is  followed  in  which  the  corals  are  divided  into  the  orders 
Rugosa,  Tabulata,  Aporosa,  and  Perforata.  The  Rugosa  had  the  septa  (or  calcareous 
plates  in  the  interior  of  the  "  cup  ")  arranged1  in  multiples  of  four,  while  in  the  other  orders 
they  were  developed  in  multiples  of  six.  This  classification  is  now  much  broken  up. 
The  tabulate  corals  (in  which  the  cup  was  crossed  horizontally  by  well-marked  floors)  are 
very  widely  dispersed,  many  being  now  relegated  to  the  Hydrozoa.  To  this  order  ffalysites, 
Favosites,  and  Monticulipora,  the  three  genera  above  mentioned,  belonged  ;  so  the  state- 
ment now  may  be  not  strictly  correct.  But  the  classification,  if  artificial,  was  very  con- 
venient, so  that  it  may  be  retained  for  purposes  of  general  description. 


A    SKETCH  OF  THE  EARTH'S  LIFE-HISTORY. 


445 


increase  in  all  the  orders  of  the  Mollusca,  and  chiefly  in  the  lamelli- 
branchs,  which  have  now  run  up  to  76  species,  being  more  abundant 
here  than  in  any  other  formation  below  the  Carboniferous  Lime- 
stone. There  are  53  species  of  gasteropods  and  47  of  cephalopods. 
The  graptolites  continue  numerous,  and  corals  are  now  fairly  common. 
Altogether  the  fauna  of  this  system  is  rich  not  only  in  genera  and 
species,  but  also  in  individuals,  for  the  blocks  of  stone  are  often 
crowded  with  fossils. 

The  fauna  of  the  Lower  Llandovery,  as  might  be  expected  from 
a  time  of  transition  and  disturbance,  is  less  rich  than  that  of  the 
Bala  or  Caradoc.  It  consists  of  only 
204  species,  or  about  one-third  the 
number  of  the  preceding  formation,  and 
exhibits  no  characteristic  which  calls 
for  special  notice.  The  Upper  Llan- 
dovery fauna  is  somewhat  richer  than 
it  in  species,  for  these  number  261. 
The  Lower  Llandovery  receives  slightly 
more  than  half  its  fauna  (105  species) 
from  the  Bala,  and  transmits  almost 
exactly  the  same  proportion  (104 
species)  to  the  Upper  Llandovery. 
This  accordingly  consists  of  about  two- 
fifths  of  the  older  fauna  and  three-fifths 
of  its  own.  In  the  Lower  Llandovery 
the  lamellibranchs  are  few  in  number, 
but  corals,  Crustacea,  and  brachiopods 
are  fairly  abundant.  In  the  Upper 
Llandovery  the  Mollusca  generally  are 
better  represented  ;  the  corals  are  in- 
creasing,  but  the  trilobites  are  now 
beginning  to  diminish  in  the  number  of  genera  and  species.  Here, 
however,  an  other  peculiar  class  of  the  Crustacea  makes  its  appearance, 
that  of  the  Merostomata.  This  is  divided  into  two  orders  :  one,  the 
Xiphosura  ("  sword-tails,"  from  the  long  spike  which  terminates  the 
carapace),  is  still  represented  by  the  living  king-crabs.  This,  how- 
ever, does  not  appear  till  the  Carboniferous  system  is  reached.  The 
other,  the  Euryptcrida,  is  first  represented  by  the  genus  Pterygotus 
in  the  Upper  Llandovery.'*  The  above  figure  (Fig.  152)  will  give 


FlG"   'S'-ECRYPTERUS 


*  In  Bohemia  they  have  been  found  in  beds  of  Ordovician  age. 


44^  THE   STORY  OF  OUR  PLANET. 

an  idea  of  the  general  appearance  of  these  creatures,  some  of  which 
had  a  superficial  resemblance  to  the  macrurous  (long-tailed)  Crustacea, 
such  as  the  lobster ;  but  from  these  they  differed  in  more  than  one 
respect,  perhaps  the  most  marked  being  that  in  the  latter  the  mas- 
ticating organs  are  aborted  legs,  and  these  are  followed  by  the 
appendages  for  locomotion,  while  in  the  Merostomata  the  same  limb 
discharges  both  functions.  In  the  Upper  Llandovery  also  the  first 
Echinids  appear.  These,  however,  like  all  the  Palaeozoic  forms, 
differ  from  the  existing  sea-urchins  in  one  important  respect,  that 
the  test  or  "  shell  "  is  composed  of  more  than  twenty  rows  of  plates  ; 
it  was,  moreover,  commonly  flexible,  a  character  which  has  been 
very  exceptional  since  that  era.  Both  these  newly  come  groups 
continue  to  be  rare  for  a  considerable  time. 

The  Wenlock  group  has  a  rich  fauna,  consisting  of  536  species. 
This  may  be  partly  due  to  the  fact  that  it  contains  some  rather 
important,  beds  of  limestone.  Corals,  both  tabulate  and  rugose,  are 
common,  and  form  small  reefs  ;  so,  too,  are  polyzoa,  but  graptolites 
are  dwindling.  Representatives  of  a  singular  group  of  Hydrozoa, 
called  Stromatoporids,  also  occur,  the  true  position  of  which  was 
for  long  uncertain.  The  calcareous  "  skeleton,"  at  first  sight, 
resembled  in  some  respects  a  foraminifer,  in  others  a  sponge,  and  in 
others  a  coral,  and  in  general  aspect  recalled  the  noted  Eozoon,  which 
has  been  already  mentioned  (p.  347).  They  occur  elsewhere  in  the 
Silurian,  but  are  rather  common  in  the  Wenlock  beds.  Crinoids 
are  numerous,  at  least  twenty  new  genera  making  their  appearance. 
This  suggests  a  migration  of  the  order,  which,  according  to  Mr. 
Etheridge,  was  probably  from  the  west.  Trilobites  are  abundant 
individually,  but  the  number  of  species  has  diminished.  The  Meros- 
tomata are  increasing,  brachiopods  are  abundant,  but  the  same  can 
hardly  be  said  of  any  of  the  true  mollusca,*  though  certain  genera, 
such  as  Euomphalus  are  far  from  rare.  The  fauna  of  the  Ludlow 
group  is  less  rich  than  that  of  the  Wenlock,  for  it  numbers  only  392 
species.  Crustaceans,  brachiopods,  and  lamellibranchs  are  the  most 
abundant  members.  The  graptolites  have  now  almost  disappeared, 
and  the  corals,  as  might  be  expected  from  the  nature  of  the  deposits, 
are  not  common.  But  the  Ludlow  beds  exhibit  one  marked  advance 
in  the  development  of  life,  for  in  them  the  first  vertebrate  animals 

*  Although  superficially  the  Brachiopoda  seem  to  be  very  closely  allied  with  the  Mollusca, 
and  are  generally  included  with  these  in  a  manual  on  that  subject,  zoologists  consider 
them  more  nearly  related  to  the  Polyzoa,  and  class  them  with  these  in  a  separate  sub- 
kingdom. 


A    SKETCH  OF    THE   EARTH'S  LIFE-HISTORY. 


447 


have  been  found.  These  are  fishes,  the  oldest  of  them  occurring  in 
the  Lower  Ludlow  stage.  This,  which  is  named  Scaphaspis  luden- 
st's,  belongs  to  the  order  of  the  ganoids — fishes  which  frequently 
were  armor-plated  ;  that  is,  protected  by  hard  bony  scales,  some- 


FIG.  153. — GANOID  FISHES  (OLD  RED  SANDSTONE). 

The  lower  one  (Coccosteus  decipiens)  shows  the  armor  plating  and  skeleton  only. 

times  covering  the  whole  body.  The  members  of  this  order  pre- 
dominated in  the  world  until  Cretaceous  times,  when  they  began  to 
wane,  and  are  now  very  scantily  and  sparsely  represented,  the  most 
familiar  form  being  the  garpike  (Lepidosteus)  of  the  North  American 
rivers.  The  Elasmobranchs,*  an  order  to  which  the  modern  sharks, 
dogfishes,  sawfishes,  and  rays  belong,  also  appear  in  the  upper  part 
of  the  Ludlow  group. 

The  Devonian  rocks  in  Britain  do  not  exhibit  a  rich  fauna.  The 
marine  or  normal  type  only  reaches  the  surface  in  the  southwest  of 
England.  The  abnormal  Old  Red  Sandstone  type,  which  covers  a 
large  area  in  these  islands,  is  not  generally  rich  in  life,  ganoid  fishes 
and  merostomatous  crustaceans  being  the  most  abundant.  In 
Ireland  a  fresh  water  bivalve — Anodonta  jukesii,  closely  allied  to  the 
living  Anodon  or  swan  mussel — has  been  found  in  the  upper  par,t  of 
the  Old  Red  Sandstone.  This  is  the  first  indubitable  fresh-water 
bivalve.  In  Canada  and  the  United  States,  strata  of  Devonian  age, 
which  are  rich  in  plants,  have  also  furnished  the  first  air-breathing 
mollusk,  Strophites  grandcevus,  and  a  few  genera  of  insects  related 
to  the  May  flies  and  dragon  flies.  The  marine  fauna  of  Britain  con- 

*A11  the  older  types  of  fish  are  "  heterocercal  " — that  is,  the  backbone  is  prolonged 
into  one  lobe  of  the  tail  fin,  which  is  larger  than  the  other. 


448 


THE   STORY  OF  OUR  PLANET. 


tains  557  species,  very  few  of  which  have  come  up  from  the  under- 
lying Silurian,  and  rather  more  than  one-twelfth  (most  of  them 
belonging  to  the  upper  part  of  the  Devonian)  pass  up  into  the  Car- 
boniferous system.  In  the  limestones,  corals — tabulate  and  rugose 
— are  abundant,  as  may  be  seen  in  the  so-called  "  Devonshire 
Marble."  They  appear  sometimes  to  have  formed  small  reefs. 
The  genera  correspond  with  those  of  the  Silurian  rather  than  of  the 


FIG.  154. — DEVONIAN  AND  CARBONIFEROUS  FOSSILS. 

(i)  Productus  semireticulatus :  (z)  Pentremites  florealis  ;  (3)   Calceola  sandal  ina  ;  (4)  Stringo- 
cephalus  burtini;  (5)  Megalodon  cucullatus  ;  (6)  Spirifer  speciosus. 

Carboniferous  strata,  but  the  species  are  usually  distinct.  A  very 
peculiar  solitary  form  called  Calceola  sandalina  for  long  perplexed 
palaeontologists.  It  was  doubtfully  referred  to  the  brachiopods, 
but  is  now  recognized  as  a  rugose  coral,  which  possesses  an  oper- 
culum,  a  very  rare  appendage.  Stromatoporids  also  are  rather 
common,  but  the  graptolites  have  now  all  but  disappeared.  None 
have  been  found  in  the  British  Devonian  rocks,  properly  so  called, 
but  one  species  has  occurred  in  a  bed  of  dark  shale  intercalated  in 
the  Lower  Old  Red  Sandstone  of  Scotland.  Of  the  Echinoderms, 
crinoids  are  fairly  common,  cystideans  are  declining,  and  an  allied 
but  equally  unsuccessful  order,  the  Blastoidea,  makes  its  appearance. 
Trilobites  are  distinctly  diminishing,  but  the  Merostomata  are  com- 
paratively common,  and  attain  a  large  size ;  one  genus,  Pterygotus, 
sometimes  grows  to  a  length  of  six  feet.  Brachiopods  are  very 
abundant,  the  genus  Spirifera,  with  its  long  hinge,  being  in  great 
force.  Some  forms,  which  present  a  general  resemblance  to  the 
living  Terebratula  (the  lamp-shell)  are  very  characteristic  of  the 
Devonian  rocks ;  one  of  the  commonest  is  the  genus  Stringocephalus, 
which,  as  the  name  (owl-head)  implies,  is  distinguished  from  a  true 


A    SKETCH  OF    THE  EARTH'S  LIFE-HISTORY.  449 

Terebratula  by  the  beak  coming  to  a  point  instead  of  being  trun- 
cated and  terminating  in  a  hole.  One  brachiopod,  Atrypa  reticu- 
laris,  which  swarms  in  the  Wenlock  Limestone,  runs  all  through 
the  Devonian  strata.  The  geographical  range  of  this  shell  is  com- 
mensurate with  its  geological,  for  it  has  been  found  in  almost  every 
quarter  of  the  globe.  The  different  classes  of  the  Mollusca  are 
fairly  represented,  and  the  presence  of  coiled  forms  of  cephalopods, 
with  characteristics  premonitory  of  the  Secondary  Ammonites  (see 
p.  435),  is  interesting.  As  a  whole,  however,  the  fauna  of  this 
period  does  not  show  any  very  marked  step  in  advance,  and  it 
clearly  occupies  a  position  intermediate  between  those  of  the  Silu- 
rian and  the  Carboniferous  systems. 

In  Great  Britain,  as  already  stated,  the  Carboniferous  system  in 
its  lower  portion  is  mainly  represented  by  strata  distinctly  marine  ; 
in  its  upper  almost  wholly  by  beds  of  fresh  water  origin  ;  but  it 
must  be  remembered  that  this  arrangement,  after  all,  is  a  local  acci- 
dent, though  it  happens  to  hold  good  in  most  of  the  regions  which, 
so  far,  have  been  more  thoroughly  examined.  The  marine  fauna  is 
a  rich  one.  Foraminifera,  hitherto  rare,  are  now  rather  common, 
and  sponges  become  much  more  abundant  than  in  any  previous 
formation.  The  Hydrozoa  are  not  strongly  represented,  but  rugose 
and  tabulate  corals  are  very  frequent,  making  small  reefs,  the  genus 
Lit  J wst  rot  ion  being  one  of  the  most  abundant  of  the  former. 
Crinoids  are  also  common  ;  the  number  of  species  is  somewhat 
large,  but,  as  individuals,  they  must  have  occurred  in  swarms. 
Some  of  the  so-called  Derbyshire  marble  is  crowded  with  portions 
of  the  stems,  with  detached  plates  from  the  bodies  and  fragments 
of  the  arms.  These  often  belong  to  one  genus,  Actinocrinus.  The 
variety  of  chert,  locally  called  screwstone,  is  full  of  casts  of  these 
stems,  the  calcareous  part  of  the  organism  having  been  removed 
from  the  siliceous  matter  by  the  action  of  water.  The  Crustacea 
have  several  representatives,  though  the  trilobites  are  all  but  gone, 
only  three  genera,  with  but  few  species,  now  remaining.  Euryp- 
terids  continue,  and  relations  of  the  king-crab  appear.  Polyzoa  are 
common,  brachiopods  are  very  abundant,  the  richest  genera  being 
Spirifera  and  Productus.  The  latter,  which  makes  its  appearance  in 
the  Devonian,  swarms  in  the  Carboniferous  Limestone,  one  species, 
P.  giganteus,  sometimes  measuring  about  twelve  inches  in  its  long- 
est diameter  ;  another  species,  P.  semireticulatus,  which  also  occurs 
very  abundantly,  is  almost  world-wide  in  its  distribution.  Blocks  of 
the  Carboniferous  Limestone  are  often  largely  composed  of  the 


45°  *HE   STORY  OF  OUR  PLANET. 

shells  of  the  one  or  the  other  species.  The  lamellibranchs  are 
very  abundant,  more  than  330  species  occurring  in  the  British  Car- 
boniferous Limestone  alone.  Gasteropods  and  cephalopods  are 
also  numerous,  and  though  neither  the  pteropods  nor  the  hetero- 
pods  are  represented  by  very  many  species,  the  genus  Conularia  in 
the  former  and  Bcllerophon  in  the  latter  are  both  well  developed. 
Fish  were  abundant  in  these  ages,  both  in  the  seas  and  in  the  rivers, 
some  of  them  attaining  a  considerable  size. 

Passing  now  to  the  more  distinctively  non-marine  Carboniferous 
fauna,  for  which  in  Britain  we  must  generally  look  rather  to  the 
upper  part  of  the  system,  little  bivalve  Crust- 
acea, related  to  the  living  Cypris — still  com- 
mon in  pools  and  slow  streams — literally 
swarmed  in  the  marshy  waters,  for  masses  of 
shale  are  often  spotted  all  over  with  their 
tiny  cases.  Representatives  of  other  orders 
are  by  no  means  unfrequent,  but  as  these 
FIG.  155.— CYPRIS.  forms  are  less  generally  familiar,  we  pass 
them  by.  Decapod  Crustacea*  (to  which  the 

crabs  and  lobsters  belong)  now  make  their  appearance,  but  at 
present  are  rare.  Scorpions  and  other  members  of  the  AracJmida 
have  been  found,  together  with  Myriapoda,  distinctly  related  to 
the  existing  centipedes,  and  insects  were  not  unfrequent  in  the 
forests  of  this  age.  They  present  resemblances  to  more  than  one 
existing  order,  but  are  referred  by  Mr.  Scudder,  the  chief  authority 
on  this  subject,  to  "a  single  homogeneous  group  of  generalized 
hexapods  which  should  be  separated  from  later  types  more  by  the 
lack  of  those  special  characteristics  which  are  the  property  of  exist- 
ing orders  than  by  any  definite  peculiarities  of  its  own."  f  Some 
seem  like  forerunners  of  May  flies,  others  of  cockroaches,  others, 
again,  of  beetles  :  the  wings  of  one  American  specimen  must  have 
measured  nearly  seven  inches  across.  The  first  representatives  of 
the  order  appear  on  the  Continent  at  an' earlier  date,  low  down 
in  the  Silurian  rocks  of  Calvados ;  a  few  occur  in  the  Devonian,  and 
they  become  rather  more  common  in  the  fresh-water  or  estuarine 
deposits  of  the  Carboniferous  system.  Fresh-water  bivalves  are 
sometimes  very  abundant,  several  of  the  genera  being  rather  nearly 
related  to  the  living  river  mussel  (Unio).  On  turning  to  the  verte- 


*  In  America  they  have  occurred  in  Devonian  rocks. 

f  Nicholson  and  Lydekker,  "  Manual  of  Paleontology,"  vol.  i.  p.  592. 


A    SKETCH  OF    THE   EARTH'S  LIFE-HISTORY.  451 

brates  we  find  that  fish  swarmed;  but  a  great  step  is  now  taken, 
and  representatives  of  a  higher  class,  the  Amphibia,  make  their 
appearance.  All  belong  to  one  order,  the  Labyrinthodonts,  so 
called  from  the  curiously  convoluted  or  labyrinthic  structure 
exhibited  by  their  teeth.  This  peculiar  dental  structure  is  also 
found  in  some  of  the  ganoid  fishes,  to  which  this  order  in  other 
respects  is  allied.  Altogether  26  species,  belonging  to  21  genera, 
have  been  identified  in  the  British  Isles.  Amphibians  also  occur 
in  other  parts  of  the  world  in  beds  of  the  same  age,  and  in  Nova 
Scotia  the  body  of  one  form  (Dendrerpeton  acadianuin),  about  three 
feet  long,  was  found  coiled  up  in  the  sand  which  had  filled  the 
hollow  trunk  of  a  Sigillarian  tree.  No  true  reptiles  have  as  yet 
been  identified  with  certainty,  although  a  little  doubt  exists  as  to  the 
proper  zoological  position  of  one  form  ;  all  probably  belong  to  the 
Amphibia. 

The  fauna  of  the  Permian  system  in  Britain  is  comparatively  poor 
and  stunted,  and  is  indicative  of  somewhat  exceptional  conditions, 
possibly  those  of  an  inland  sea,  like  the  Caspian,  or  of  one  which 
communicated  with  the  open  ocean  by  a  rather  narrow  strait,  like 
the  Black  Sea.  It  has  a  closer  relationship,  on  the  whole,  with  the 
fauna  of  the  Carboniferous  system  than  with  that  of  the  Trias. 
Sponges,  foraminifers,  corals,  echinids,  annelids,  and  Crustacea  are 
but  poorly  represented.  No  trilobite  has  been  discovered  in  any 
British  deposit  of  this  age,  the  last  having  been  found  in  a  bed  in 
the  Millstone  Grit,  but  one  genus  (Phillip sid)  has  occurred  in  the 
Permian  deposits  of  Russia,  and  of  North  America.  Polyzoa  are 
sometimes  numerous,  and  brachiopods  fairly  represented  ;  so  also 
are  lamellibranchs  and  gasteropods,  but  both  the  pteropods  and  the 
cephalopods  contribute  only  a  single  genus  each.  Some  fishes  and 
amphibians  are  found,  and  the  first  indubitable  reptile  (Protero- 
saiirns]  makes  its  appearance.  In  other  parts  of  the  world  a  much 
richer  fauna  characterizes  the  Permian  deposits,  as,  for  instance,  in 
Russia,  the  Southeastern  Alps,  Sicily,  and  in  parts  of  Asia  and 
North  America.  It  exhibits  distinctly  a  transitional  character.  Not 
a  few  well-known  Carboniferous  forms,  such  as  the  foraminifer  Fusn- 
lina,  the  brachiopods  Producttis,  Orthis,  Leptcena,  and  other  well- 
known  Primary  genera,  are  common,  together  with  species  of  Bel- 
lerophon,  and  such  cephalopods  as  Orthoceras,  but  among  the  lamel- 
libranchs several  genera  of  a  newer  type  appear,  and  cephalopods 
closely  allied  to  the  Secondary  Ammonites  occur  frequently  in  the 
Asiatic  Permians. 


45 2  THE    STORY  OF  OUR  PLANET. 

Casting  a  retrospective  glance  over  the  fauna  of  the  Primary  or 
Palaeozoic  era,  we  find  that,  practically,  all  the  more  important 
classes  and  orders  from  the  Reptilia  downward  are  represented,  and 
that  the  latter  evidently  are  coming  upon  the  scene  as  the  era  is 
drawing  near  to  its  close.  We  also  notice  that  the  development  of 
life  exhibits  a  gradual  and  fairly  uniform  progress,  and  that  the 
earlier  forms  of  any  class  or  order  are  more  generalized  than  those 
most  nearly  allied  to  the  species  which  are  still  in  existence  ;  that 
is  to  say,  they  in  one  unite  characters  which  are  now  exhibited  by 
separate  types,  and  thus  often  resemble  more  closely  the  embryonic 
than  the  adult  forms  of  creatures  which  are  now  living.  The  imper- 
fection of  the  data  on  which  inferences  are  grounded  must  never  be 
forgotten  ;  the  idea  of  an  extinct  flora  or  fauna  in  many  cases  has  to 
be  obtained  from  comparatively  limited  areas,  in  which  deposits 
may  have  occurred,  as  with  the  Coal  Measures  or  the  Old  Red 
Sandstones,  under  rather  exceptional  conditions.  Still,  even  if 
every  allowance  be  made  for  such  difficulties,  the  absence  of  some 
of  the  more  highly  developed  forms  of  life  from  these  ancient 
deposits  may  be  regarded  as  a  certainty,  and  the  proportion  among 
those  which  did  exist  was  very  different  from  that  now  prevalent  in 
the  globe.  Restricting  ourselves  to  the  fauna  only,  we  may  venture 
to  affirm  that  there  were  neither  birds  nor  mammals;  amphibia 
were  not  common;  reptiles  only  just  beginning  their  career;  and 
the  fishes  mostly  belong  to  orders  which  since  then  have  dwindled 
or  have  become  extinct.  Certain  abnormal  hydrozoa  and  corals 
referred  to  the  rugose  and  tabulate  orders  took  the  place  of  those 
which  now  tenant  the  warmer  seas.  Crinoids  were  more"  common 
than  sea-urchins  and  starfishes ;  trilobites  are  found  instead  of 
crabs,  lobsters,  and  shrimps.  Until  the  Carboniferous  period  none 
of  the  true  mollusca  were  very  abundant,  the  brachiopods  taking 
their  place.  Some  of  the  orders,  most  of  the  genera,  all  the  species 
of  the  Primary  era  have  now  disappeared. 

The  changes  foreshadowed  in  the  Permian  are  carried  much 
further  in  the  Trias.  On  this  subject  the  British  Islands  supply 
but  little  information  to  the  geologist.  The  Bunter  group  is  prob- 
ably destitute  of  fossils;  the  Keuper  contains  but  few;  the  Rha^tic 
beds  are  thin,  and  far  from  rich  in  organic  remains.  But  the  gap 
in  our  knowledge,  due  to  the  abnormal  conditions  which  have  been 
already  mentioned,*  is  filled  up  in  other  countries.  The  marine 

*P!>.  370-378. 


A    SKETCH  OF  THE  EARTH'S  LIFE-HISTORY.  453 

beds  (muschelkalK)  intercalated  between  the  Bunter  and  the  Keuper 
in  Lorraine,  Alsace,  and  the  adjacent  parts  of  Germany  contain  a 
fair  number  of  fossils,  but  the  Trias  of  the  Eastern  Alps  is  altogether 
a  marine  series,  and  is  much  richer  in  organic  remains.  Beds  of 
this  type  may  be  traced,  not  only  throughout  the  Mediterranean 
area,  but  also  in  various  parts  of  Asia,  America,  and  even  in  New 
Zealand  and  Australasia.  In  these  neither  foraminifers  nor  sponges 
can  be  called  very  common.  Certain  crinoids  are  rather  numerous, 
such  as  the  genus  Encrinus,  but  the  characteristic  Palaeozoic  types 
have  disappeared.  Echinoids  of  the  normal  aspect  now  begin  to 
be  frequently  found,  among  them  the  genus  Cidaris,  which  still 
exists  in  the  warmer  seas,  though  a  few  of  the  peculiar  older  forms 
yet  linger.  Brachiopods  are  relatively  less  numerous  than  hereto- 
fore ;  the  Palaeozoic  forms  are  either  dwindling  or  have  already 
gone ;  the  genera  Terebratula  and  Rkynchonclla,  which  have  been 
long  in  existence  and  still  survive,  now  assume  a  greater  importance. 
The  lamellibranchs,  however,  appear  to  be  elbowing  these  humbler 
bivalves  out  of  the  way.  Many  genera,  very  characteristic  of  the 
Secondary  rocks — some  extinct,  as  Monotis,  Halobia,  and  Gervillia; 
others  still  living,  such  as  Pecten,  Lima,  and  Cardita — are  now  abun- 
dant, and  give  a  marked  character  to  the  fossils  of  this  period.  Gas- 
teropods  also  are  plentiful,  showing  a  mixture  of  old  and  new  types  ; 
so  too  are  cephalopods.  The  Palaeozoic  Orthoceras  brings  its  long 
career  to  an  end  ;  Nautilus  continues,  but  the  most  interesting  forms 
are  the  representatives  of  the  Ammonites.  The  transitional  Cera- 
tites,  with  its  peculiar  sutures  exhibiting  alternating  saddles  and 
lobes  slightly  denticulated  (see  Fig.  145  £),  practically  characterizes 
the  Trias,  and  is  the  immediate  forerunner  of  the  great  family  of 
the  Ammonites,  which,  as  already  mentioned,  swarm  in  many  of  the 
Secondary  rocks ;  of  these  also  a  few  actual  representatives  are 
found  in  Triassic  strata.  Fish  are  fairly  numerous,  and  among  them 
"  the  oldest  representatives  of  the  bony  fishes,  or  Teleostei,  which  is 
now  the  most  predominant  group,"  probably  occur.  Amphibia 
seem  to  have  been  rather  abundant,  and  some  of  the  Labyrintho- 
donts  attained  a  large  size,  being,  perhaps,  seven  or  eight  feet  in 
length.  Their  footprints  are  not  uncommon  on  some  of  the  flaggy 
sandstones  in  various  parts  of  England.*  Certain  of  these  present 
a  rude  resemblance  to  the  mark  of  a  gigantic  human  hand,  whence 
the  name  Cheirotherium  (hand-beast)  was  formerly  given  (Fig.  135). 

*  Especially  in  Cheshire  and  the  adjoining  counties. 


454  THE   STORY  OF  OUR  PLACET. 

These  tracks,  however,  and  the  animals  which  made  them,  have  not 
as  yet  been  coupled  together  with  any  certainty,  and  it  is  possible 
that  some  may  be  the  imprints  of  true  reptiles.  These  "  were  very 
abundant  in  the  Trias,  especially  in  comparison  with  the  Permian. 
Almost  all  the  groups  characteristic  of  Mesozoic  times  had  their 
representatives  in  the  Trias."  *  But  as  they  do  not  become  common 
in  England  till  the  next  period,  it  will  be  more  convenient  to  abstain, 
for  the  present,  from  entering  into  details.  Certain  tracks  in  the 
Triassic  sandstones  of  Connecticut,  which  formerly  were  supposed 
to  have  been  made  by  birds,  are  now  referred  to  reptiles.  But 
though  the  existence  of  the  former  in  Triassic  times  has  not  yet 
been  established,  the  occurrence  of  mammals  cannot  be  questioned ; 
these  have  occurred  higher  up  in  the  Keuper — both  in  the  neighbor- 
hood of  Stuttgart  and  in  Somersetshire ;  others  have  been  found  in 
beds,  presumably  of  the  same  age,  in  North  Carolina  and  in  South 
Africa ;  mammalian  remains  also  have  been  occasionally  met  with 
in  beds  of  Rhaetic  age  in  England  and  in  other  countries.  All  these 
earlier  forms  were  "  of  small  size,  and  apparently  more  or  less 
closely  allied  to  the  existing  marsupials,  and  probably  also  to  the 
monotremes,  and  perhaps  the  insectivores."  f  The  Anglo-German 
form  Microlestes  (little  thief)  was  a  small  predaceous  creature,  the 
exact  relationships  of  which  are  uncertain,  for  at  present  it  is 
known  only  by  its  teeth.  The  South  African  Dromatherium  (run- 
ning beast)  was  larger.  As  this  "  exhibits  some  curious  approxima- 
tions in  the  structure  of  its  teeth  to  reptiles  and  amphibians,"  it 
may  be  an  ancestral  type  of  the  mammals. 

The  Jurassic  rocks,  both  in  Britain  and  in  the  western  parts  of 
Europe,  exhibit  a  great  variety  of  materials,  and  contain  abundant 
remains  of  a  flora  and  a  fauna.  The  deposits,  though  on  the  whole 
marine,  were  in  many  cases  formed  in  the  vicinity  of  the  land,  and 
occasionally  indicate  a  terrestrial  origin.  On  this  account  the  fauna 
exhibits  corresponding  variations ;  no  one  would  expect  to  meet 
with  a  coral  reef  in  a  clay  bed,  or  river  mussels  in  a  deep-sea  lime- 
stone. But  as  our  space  is  limited,  we  must  speak  of  it  as  a  whole, 
without  dwelling  on  details  or  separately  describing  the  tenants  of 

*  Kayser  and  Lake,  "  Text-book  of  Comparative  Geology,"  p.  233. 

f  Nicholson  and  Lydekker,  "  Manual  of  Palaeontology,"  ch.  Iviii.  The  monotremes 
are  a  very  low  type  of  mammals,  obtaining  the  name  from  the  fact  that  the  urine  and  the 
faeces  are  discharged  by  a  single  outlet.  The  Ornithorhynchus  or  duck-billed  platypus  of 
Australia  is  one  of  the  few  living  representatives  of  the  order.  The  marsupials  (pouched 
animals)  are  represented  by  the  kangaroos  and  opossums  ;  the  moles  and  shrews  belong 
to  the  insectivores. 


A    SKETCH  OF    THE  EARTH'S  LIFE-HISTORY. 


455 


the  land  and  of  the  sea.  Foraminifera  are  not  rare ;  sponges  are 
often  common  ;  corals  are  sometimes  very  abundant ;  they  belong 
chiefly  to  the  aporose  division,  several  of  them  being  more  or  less 
nearly  allied  to  the  star-coral  and  brain-coral  of  the  present  day,  for 
the  old  tabulata  and  rugosa  have  disappeared  ;  they  occasionally 


FIG.  156. — PENTACRINUS  BRIAPVE-JS  (E-XTRACRINUS). 

a.  Reduced  in   size,      b,  Body  and   parts   of  arms,   natural  size. 

form  reefs,  but  some  smaller  solitary  corals  are  also  frequent.  Sea- 
urchins  abound  ;  most  of  them  belong  to  extinct  genera,  but  all 
possess  the  usual  twenty  rows  of  plates,  and  represent  both  the 
regular  group  (more  or  less  circular  in  form)  and  the  irregular  group 
(often  heart-  or  shield-shaped);  a  few,  however — as,  for  instance, 
Cidaris — still  exist  on  the  earth.  Sea-lilies  are  less  abundant  on  the 
whole,  though  the  beautiful  Pentacrinus  (Fig.  156) — a  genus  which 


456 


THE   STORY  OF  OUR  PLANET. 


still  lives — seems  to  have  swarmed  in  some  localities  on  the  sea 
bottom  during  the  earlier  part  of  the  Liassic  epoch — for  often  a 
dozen  specimens  may  be  counted  on  the  surface 
of  a  slab  considerably  less  than  a  square  foot  in 
area.  In  this,  as  in  a  large  number  of  the  more 
modern  crinoids,  the  joints  of  the  stem  are  pent- 
angular in  outline ;  but  forms  with  a  rounded 
stem,  like  the  Palaeozoic  crinoids,  are  also  found, 
as,  for  instance,  Apiocrinus  (Fig.  157),  which  is 
rather  abundant  at  a  somewhat  later  time,  about 
the  middle  of  the  Lower  Oolite.  The  crustacean 
fauna  includes  both  long-tailed  and  short-tailed 
members,  and  this,  as  well  as  the  insect  fauna,  is 
fairly  rich.  A  very  marked  change  has  passed 
over  the  brachiopods.  The  characteristic  Palae- 
ozoic genera,  such  as  Orthis,  Atrypa,  Pentamerns, 
Product  us,  etc.,  have  disappeared ;  Leptcena  and 
Spirifera  struggle  on  into  the  lower  part  of  the 
Jurassic  system  and  then  vanish.  RJiynchonclla 
and  Terebratula,  with  a  group  of  genera  closely 
allied  to  it,  dominate  over  all  the  others,  being 
represented  by  many  species  and  by  swarms  of 
individuals.  The  lamellibranchs  have  now  ob- 
tained the  footing  in  the  world  which  they  have 
kept  ever  since — genera,  species,  individuals,  all 
are  numerous.  Many  genera,  which  are  still 
abundant,  had  already  risen  to  a  great  impor- 
tance, such  as  Ostrea  (the  oyster), 
with  several  of  its  allies,  as  Gryplicca 
and  Exogyra,  also  Lima,  Pecten  (fan- 
shell),  Avicula*  Gervillia  (extinct),  and 
Trigonia.  Genera  allied  to  the  living 
Anatina  (lantern-shell),  such  as  the 
existing  Pholadomya,  and  the  extinct 
Ceromya,  Goniomya,  and  Myacites,  are 
frequent  in  the  more  calcareous  rocks. 
The  gasteropods  also  are  richly  repre- 
sented :  among  the  most  characteristic 
are  trochus-like  shells,  such  as  Pleuro- 
tomaria  (extinct),  and  elongated  spiral  shells,  which  take  the  general 

*  The  "  pearl-oyster"  is  an  Arictila. 


FIG.  157. — APIOCRINUS 
(JURASSIC). 


A    SKETCH  OF   THE  EARTH'S  LIFE-HISTORY.  457 

outline  of  the  living  Turritella  (cockspur),  such  as  Ceritkium, 
Chemnitzia,  Nermea,  with  its  curious  internal  ridges,  which  render 
the  genus  so  easy  of  recognition;  and  winged  shells,  such  as 
Pteroceras  and  Alaria,  resembling  the  Aporrhais  (bat's-wing),  still 
found  on  British  shores. 

But  the  more  marked  characteristic  of  the  Jurassic  molluscan 
fauna  is  the  abundance  of  representatives  of  the  cephalpods.  The 
one  group,  Belemnites*  is  distantly  related  to  the  living  cuttlefishes. 


FIG.  158.— SHELL  OF  A  TRIGONIA  (RECENT). 

The  genus,  which  makes  its  appearance  in  the  continental  Trias, 
abounds  in  strata  of  Jurassic  age.  The  number  of  individuals  must 
have  been  very  great.  The  shells  sometimes  lie  in  layers,  so  that 
the  bed  of  the  sea  must  have  been  strewn  with  them.  The  other 
group  is  that  included  in  the  old  genus  Ammonites.  Members  of 
this  occur  in  even  greater  profusion  than  the  belemnites;  the  differ- 
ent species  vary  greatly  in  size:  more  commonly  they  run  from 
about  four  inches  in  diameter  downward,  but  about  double  this  is 
reached  by  a  fair  number  of  species,  and  a  gigantic  form  is  occasion- 
ally met  with,  measuring  perhaps  a  couple  of  feet  across.  The 
nautilus  keeps  on  the  even  tenor  of  its  way,  but  these  newcomers 
quite  throw  it  into  the  shade  in  their  brilliant  but  not  very  durable 
career. 

But  in  the  Jurassic  period  the  vertebrate  fauna  becomes  more 
important  than  it  hitherto  has  been.  The  fish  still  continue  to  be 
mainly  ganoid,  but  as  the  older  heterocercal  forms  have  almost  dis- 
appeared, they  present  a  closer  resemblance  to  those  which  are  now 
in  existence.  Mammals  continue,  but  their  remains  are  seldom 

*The  shell  is  long,  somewhat  conical,  and  pointed  at  one  end  ;  the  other  opens  out  into 
a  wineglass  shape  and  the  lower  part  is  partitioned  off  by  septa.  In  this  the  more  impor- 
tant organs  of  the  body  were  lodged,  and  the  shell,  like  that  of  the  cuttlefish,  was  partly, 
if  not  wholly,  internal.  Commonly  it  does  not  exceed  a  few  inches  in  length,  but  speci- 
mens measuring  nearly  three  feet  are  known.  Workmen  sometimes  call  them  thunderbolts. 


45 8  THE   STORY  OF  OUR  PLANET. 

found,  and  the  representatives  of  this  class  appear  not  to  have 
departed  far  from  the  original  Triassic  types,  being  small  in  size,  and 
allied  to  the  monotremes  and  marsupials  of  the  present  day.  In 
England  two  or  three  have  been  found  in  the  "  Stonesfield  slate," 
a  local  deposit  underneath  the  Bath  Oolitic  Limestone,  i.  t.,  about 
the  middle  of  the  Lower  Oolite,  and  a  larger  number  in  the  Purbeck 
beds,  which  are  at  the  very  top  of  the  Jurassic  system.  Birds  also 
make  their  appearance,  though  evidently  not  in  great  numbers. 
The  earliest  one  known,  called  Arcliceopteryx,  has  occurred  in  a 
muddy  limestone  at  Solenhofen,  in  Bavaria,  of  about  the  same  age 
as  the  Kimeridge  Clay  of  England.  This  most  instructive  form 
may  be  called  a  true  bird,  for  "  the  feathers,  the  closed  skull,  and  the 
structure  of  the  foot  are  sufficient  proof  of  this.  The  biconcave 
vertebrae,  however,  the  sclerotic  ring  of  the  eye,  the  teeth,  the  long 
lizard-like  tail,  the  very  thin  ribs,  pointed  at  the  end,  the  presence  of 
twelve  to  thirteen  pairs  of  abdominal  ribs,  the  three  free  claw-bear- 
ing fingers  of  the  anterior  limb,  etc.,  are  characters  which  are  partly 
of  an  embryonic  nature,  partly  characteristic  of  reptiles,  so  that  this 
remarkable  animal  bridges  over  in  a  great  measure  the  large  gap 
existing  at  present  between  birds  and  reptiles."  * 

But  the  most  characteristic  feature  of  the  Jurassic  rocks  is  the 
extraordinary  development  of  the  latter  class.  Reptiles  occur  no 
doubt  sparsely  in  the  British  Trias.  They  are  much  more  abun- 
dant in  continental  and  foreign  deposits,  but  with  the  commence- 
ment of  the  Jurassic  period  they  became  generally  common,  both 
on  land  and  in  sea.  Chelonians  (tortoises  and  turtles)  increased  in 
number,  and  so  did  representatives  of  the  crocodiles,  though  these 
differed  from  existing  genera  in  retaining  some  embryonic  character- 
istics. But  the  most  abundant  reptiles  in  the  earlier  part  of  the 
Jurassic  period  were  marine,  Ichthyosaurus  (fish-lizard)  and  Plcsio- 
saurus  (neighbor-lizard)  being  the  most  important  genera  ;  the  former, 
a  huge  creature,  sometimes  more  than  thirty  feet  in  length,  with 
tremendous  jaws  armed  with  strong  conical  teeth,  was  powerfully 
built,  as  shown  in  the  diagram  (Fig.  159),  and  was  propelled  by  four 
paddles  and  its  strong  tail,  which  was  terminated  by  a  broad  triangu- 
lar fin,  like  that  of  a  fish,  into  the  lower  lobe  of  which  the  backbone 
appears  to  have  been  prolonged.  The  creature  in  general  shape 
slightly  resembled  a  whale,  and  was  an  air  breather,  but  it  had  a 

*  Kayser  and  Lake's  "  Text-book  of  Comparative  Geology,"  p.  278.  Two  specimens 
have  as  yet  been  found— one  is  in  the  British  Museum,  the  other  (and  more  perfect)  is 
that  at  Berlin. 


A    SKETCH  OF   THE  EARTH'S  LIFE-HISTORY. 


459 


dorsal  fin,  like  a  fish.  It  appears,  however,  to  have  been  viviparous, 
for  in  one  case  the  skeletons  of  seven  very  small  Ichthyosauri,  all  of 
the  same  size,  were  discovered  within  that  of  a  large  one.  The  eye 
was  large,  and  fitted  with 
an  arrangement  of  bony 
plates,  the  presence  of 
which  probably  not  only 
protected  the  eye  from 
pressure  in  deeper  water, 
but  also  served  to  modify 
the  curvature  of  the  lens 
and  to  adjust  the  focus  for 
seeing  near  or  distant  ob- 
jects. The  Plesiosaurus 
had  a  much  smaller  head^ 
furnished  with  sharp  but 
less  formidable  teeth, 
placed  above  a  long  neck. 
The  tail  was  shorter  and 
the  paddles  were  more 
slender  than  in  IcJithyo- 
saurus.  It  was  a  less 
powerful  animal  than  this, 
but  its  lithe  neck,  pliable 
as  that  of  a  swan,  must 
have  enabled  it  to  grope 
after  its  prey  in  the  shal- 
lower waters,  or  to  strike 
readily  in  all  directions  as 
it  swam  swiftly  along, 
while  the  Ichthyosaurus 
probably  dashed  like  a 
shark  at  its  victim.  We 
can  imagine  a  shoal  of  the 

scaly  ganoid  fishes  scattering  before  its  charge,  like  roach  from  the 
rush  of  a  pike  at  the  present  day.  There  were,  however,  other 
tyrants  of  the  seas  more  formidable  than  the  Ichthyosaurus^  but  ap- 
parently much  less  common  ;  these  belong  rather  to  the  later  part 
of  the  Jurassic.  One  of  them,  the  genus  Pliosaurus  (more  nearly  a 
lizard),  must  have  been  a  huge  creature,  for  the  jaw  is  nearly  six 
feet  long,  with  pointed  teeth  measuring  three  or  four  inches. 


460  THE   STORy  Of  OUR  PLANET. 

Another  important  order  of  reptiles,  that  of  the  Dinosaurs,  rapidly 
increases  in  importance  during  the  Jurassic  period.  These  were 
sometimes  terrestrial,  sometimes  semi-aquatic,  and  many  of  them 
attained  to  a  huge  size.  The  European  forms  are  remarkable 
enough,  but  America  has  furnished  types  yet  more  singular  and 
gigantic.  The  limbs,  as  a  rule,  are  longer  and  stronger  than  in 
modern  lizards.  One  group,  which  attains  to  a  greater  size  than  the 
other,  had  a  long  tail  and  neck,  with  a  head,  on  the  whole,  relatively 
small,  while  the  proportions  of  the  middle  part  of  the  body  were 
not  very  different  from  those  of  an  ordinary  mammal.  In  the  other 
group  the  neck  was  shorter  and  the  head  somewhat  larger,  while 
the  fore  limbs  were  considerably  smaller  than  the  hind  legs,  so  that 
probably  the  creature  frequently  sat  up  like  a  kangaroo,  and  may 
even  have  hopped  along  in  the  same  way.  Of  the  former  group 
the  largest  English  representative  is  the  Cetiosaurus  (whale-lizard), 
which  probably  was  about  fifty  feet  in  length,  and  must  have  stood 
about  ten  feet  in  height,  for  the  thigh  bone  occasionally  is  nearly 
five  feet  long.*  But  its  American  allies  Brontosaurus  (thunder- 
lizard)  and  Atlantosaurus  (Atlantic-lizard)  were  on  a  yet  vaster  scale, 
for  a  thigh  bone  of  the  latter  has  been  discovered  which  is  a  little 
over  six  feet  in  length.  Brontosaurus  was  not  quite  so  huge,  but 
"  it  was  nearly  sixty  feet  long,  and  probably  when  alive  weighed 
more  than  twenty  tons.  That  it  was  a  stupid,  slow-moving  reptile 
may  be  inferred  from  its  very  small  brain  and  slender  spinal 
cord.  .  .  No  bony  plates  or  spines  have  been  discovered  with  the 
remains  of  this  monster,  so  that  we  are  driven  to  conclude  that  it 
was  wholly  without  armor;  and,  moreover,  there  seem  to  be  no 
signs  of  offensive  weapons  of  any  kind.  Professor  Marsh  concludes 
that  it  was  more  or  less  amphibious  in  its  habits,  and  that  it  fed  upon 
aquatic  plants  and  other  succulent  vegetation.  Its  remains,  he  says, 
are  generally  found  in  localities  where  the  animal  had  evidently 
become  mired,  just  as  cattle  at  the  present  day  sometimes  become 
hopelessly  fixed  in  a  swampy  place  on  the  margin  of  a  lake  or  river. 
Each  track  made  by  the  creature  in  walking  occupied  one  square 
yard  in  extent."  f 

*  Found  in  the  upper  part  of  the  Lower  Oolite.     Phillips'  "  Geology  of  Oxford,"  ch.  xi. 

f  Quoted  from  Mr.  H.  N.  Hutchinson's  "  Extinct  Monsters,"  p.  64,  where  a  figure  of 
the  skeleton  and  a  restoration  of  the  creature  is  given.  This  pleasantly  written  volume 
gives  a  very  good  account,  founded  on  the  works  of  Professors  O.  C.  Marsh,  E.  D.  Cope, 
Owen,  and  other  authorities,  of  the  monstrous  vertebrates  of  olden  time,  with  some  excel- 
lent pictures  of  their  probable  appearance. 


A    SKETCH  OF    THE  EARTH'S  LIFE-HISTORY.  461 

Of  the  other  group  of  the  Dinosaurs  some  were  herbivorous, 
some  carnivorous.  The  former  are  represented  in  England  by 
more  than  one  form,  the  earliest  being  Scelidosaurus  (leg-lizard)* 
from  the  Lias.  It  was  probably  amphibious  in  habit,  not  less  than 
twelve  feet  long,  and  distinguished  by  carrying  "two  big  spines,  one 
placed  on  each  shoulder,  and  a  series  of  long  plates,  arranged  in 
lines  along  the  back  and  side."  Stranger  still  is  Stegosaiirus  (roof- 
lizard),  of  which  some  fragmentary  remains  have  occurred  in  the 
Upper  Oolite  of  this  country,  but  far  more  complete  materials  have 
been  obtained  in  America,  from  which  Professor  Marsh  has  been 
able  to  give  a  complete  restoration  of  this  singular  animal.  It  had 
a  remarkably  small  head  and  short  neck,  with  the  usual  large  hind 
legs  and  long  tail.  On  the  middle  of  the  back,  from  immediately 
behind  the  head,  and  continuing  to  rather  more  than  halfway  down 
the  tail,  it  bore  a  practically  continuous  row  of  bony  plates,  which, 
toward  the  middle,  became  pentagonal  or  rudely  triangular  in  out- 
line, and  attained  a  diameter  of  from  two  to  three  feet.  When  these 
came  to  an  end  their  place  was  taken  by  four  pairs  of  strong  spines, 
the  first  of  which  was  quite  two  feet  long.  Stegosanrus  exhibits 
another  most  singular  characteristic.  This  is  "  a  large  chamber  in 
the  sacrum, f  formed  by  an  enlargement  of  the  spinal  cord.  The 
chamber  strongly  resembled  the  brain-case  in  the  skull,  but  was 
about  ten  times  as  large.  So  this  anomalous  monster  had  two  sets 
of  brains,  one  in  its  skull  and  the  other  in  the  region  of  its  haunches  ! 
and  the  latter,  in  directing  the  movements  of  the  huge  hind  limbs 
and  tail,  did  a  large  share  of  the  work.":}:  Perhaps  the  favorite 
method  of  scholastic  stimulation  adopted  by  educationalists  of  the 
type  of  Busby  was  an  unconscious  recognition  of  the  possible  sur- 
vival of  some  such  structure  in  immature  humanity.  In  the  great 
doctor's  day  not  a  few  schoolboys  would  have  been  thankful  for  the 
protective  armor  of  Stegosaurns. 

Carnivorous  Dinosaurs  are  represented  by  the  formidable  Megalo- 
saurus  (great-lizard).  Its  remains  occur  throughout  the  Jurassic 
rocks  from  the  Lias  upward,  and  it  survived  that  period.§  It  had 
one  element  of  a  long  existence,  in  days  when  the  weakest  went  to  the 
wall,  for  it  was  well  able  to  take  care  of  itself.  In  length  it  attained 

*  So  named  by  Professor  Owen  because  of  its  strong  hind  legs. 

f  The  vertebrae  (usually  joined  together)  which  are  united  with  the  haunch  bones  to  form 
the  pelvis. 

\  H.  N.  Hutchinson,  "  Extinct  Monsters,"  p.  104. 

§  Its  form  had  a  general  resemblance  to  that  of  Iguanodon.     (See  Fig.  162,  p.  467). 


462  THE   STORY  OF  OUR  PLANET. 

about  thirty  feet ;  it  had  strong  hind  limbs,  formidable  claws  to  its 
feet,  and  jaws  furnished  with  long,  conical,  slightly  curved  teeth. 
It  probably  was  an  active  animal,  as  terrible  on  land  as  the  Ichthy- 
osaurus in  the  sea.  No  wonder  the  mammals  continued  small  and 
lowly  in  organization  so  long  as  these  ferocious  brutes  existed  !  But 
"  such  small  deer"  can  hardly  have  satisfied  them  ;  very  likely  the 
younger  herbivorous  Dinosaurs  had  to  keep  a  sharp  lookout,  and 
cannibalism  may  not  have  been  unknown,  when  other  food  was 
scarce. 

The  structure  of  the  Dinosaurs  is  anomalous  in  more  than  one 
respect,  and  the  precise  position  of  the  order  in  the  animal  king- 
dom is  not  easily  determined.  Of  the  little  CompsognatJius  (elegant- 
jaws),  from  the  Lithographic  Stone  of  Solenhofen  (Upper  Oolite), 
Professor  Huxley  remarks :  "  It  is  impossible  to  look  at  the  conforma- 
tion of  this  strange  reptile  and  to  doubt  that  it  hopped  or  walked  in 
an  erect  or  semi-erect  position,  after  the  manner  of  a  bird,  to  which 
its  long  neck,  slight  head,  and  small  anterior  limbs  must  have  given 
it  an  extraordinary  resemblance."  *  The  structure  also  of  the  bones 
in  Dinosaurs  frequently  approximates  to  that  of  birds,  and  the  skel- 
eton exhibits  other  characters  which  are  distinctly  avian.  Professor 
Huxley  considers  them  as  the  progenitors  of  birds,  and  Professor 
H.  G.  Seeley,  who  has  devoted  many  years  to  the  study  of  the  order, 
maintains  that  they  cannot  be  regarded  as  reptiles  in  the  ordinary 
sense  of  the  term.  Nevertheless  in  other  respects  they  resemble 
the  lizards  and  crocodiles,  so  that  in  them,  as  in  so  many  other  of 
these  earlier  creatures,  characteristics  are  united  which  are  now 
divided  among  widely  separated  forms  of  life.  ArcJiceoptcryx,  with 
its  long  tail  and  teeth,  as  well  as  some  of  the  earlier  birds,  also  den- 
tigerous,  undoubtedly  suggest  that  their  relationship  with  the 
Dinosaurs  is  far  from  being  distant. 

Flying  dragons  are  common  in  legendary  lore ;  cockatrices, 
griffins,  wyverns  figure  in  heraldry  among  "  collections  of  fabulous 
animals."  Yet  creatures  of  the  kind  lived  among  the  "  dragons  in 
the  prime,"  though,  strangely  enough,  they  ceased  to  exist  long 
ages  before  man  appeared  upon  the  earth.  The  Pterodactyles, 
or  wing-fingered  lizards,  forming  the  order  OrnitJiosauria  (bird- 
lizards),  are  found  in  the  Liassic  rocks,  and  continue  through  the 
remainder  of  the  Secondary  series.  They  become  more  abundant 
in  the  later  part  of  the  Jurassic  and  the  following  systems,  and  as 

*  Quoted  in  "  Extinct  Monsters,"  p.  80. 


A    SKETCH  OF   THE  EARTH'S  LIFE-HISTORY.  463 

they  increase  in  number  so  do  they,  on  the  whole,  in  size.  As  to 
the  latter,  different  members  of  the  family  vary  greatly.  Some 
were  hardly  bigger  than  sparrows,  the  wings  of  others  had  a  span 
of  about  twenty-five  feet.  In  many  respects  they  resembled  birds; 
the  bones  are  often  hollow ;  the  breast  bone  has  a  keel ;  the  skull 


FIG.  160.— PTERODACTYLUS  BREVIROSTRIS. 

also,  in  the  position  of  the  nostrils,  the  character  of  the  eye,  and  in 
other  respects,  suggests  avian  affinities.  The  jaws  are  long,  power- 
ful, and  armed  with  sharp,  flattish,  slightly  curved  teeth  ;  the  fore 
limbs  terminate  in  four  fingers  or  toes,  three  being  furnished  with 
claws,  and  the  other,  or  outer  one,  prolonged  to  a  great  length,  to 
support  a  membranous  wing,  somewhat  like  that  of  a  bat.  This 
mammal,  however,  has  five  fingers,  and  four  of  them  are  elongated 
to  carry  the  wing.  The  members  of  the  Ornithosaurian  order,  as 
Mr.  Lydekker  truly  observes,  are  among  the  most  remarkable  and 
strange  reptilian  forms  that  Palaeontology  has  revealed  to  us.  Some 
authorities,  indeed,  have  proposed  to  place  them  in  a  distinct  class. 
They  are,  however,  in  his  opinion,  essentially  reptiles,  and  the 
resemblances,  striking  though  they  may  be,  are  probably  "  mainly 
due  to  adaptation  for  a  similar  mode  of  life,  since  it  seems  clear 
that  the  Pterodactyles  are  altogether  off  the  direct  line  of  the  avian 
pedigree."* 

We  have  dwelt  at  some  length   on  the    Jurassic   fauna,  since  it 
presents  us  in  Britain  with  so  many  new  and  interesting  types.    But 

*  "  Manual  of  Palaeontology,"  p.  1198. 


464  THE    STORY  OF  OUR  PLANET. 

this  enables  us  to  pass  more  rapidly  over  the  remainder  of  the 
Secondary  series,  and  for  that  purpose  to  group  together  the  Neo- 
comian  and  Cretaceous  systems,  since  their  faunas  have  a  general 
resemblance  to  each  other,  though  they  seem  to  differ  sufficiently 
to  justify  a  distinction  by  separate  names.  The  English  represen- 
tatives, both  of  the  one  and  of  the  other,  are  somewhat  abnormal ; 
for  in  the  lower  part  of  the  former  we  find,  in  the  southeast  of  Eng- 
land, the  fresh-water  deposits  of  the  Weald,  and  in  the  upper  and 
major  part  of  the  other  the  White  Chalk,  a  very  pure  and  rather 
deep-sea  deposit. 

The  marine  invertebrate  fauna  does  not  call  for  many  remarks. 
As  it  departs  gradually  from  the  Jurassic  facies,  it  approaches  some- 
what to  that  characteristic  of  the  present  age.  Foraminifera  are 
occasionally  very  abundant,  as  Orbitolina  in  the  limestone  of  the 
Upper  Neocomian  in  the  Alps,  and  as  in  the  Chalk  of  Northwestern 
Europe  ;  sponges  also  are  often  very  common,  as,  for  instance,  in  the 
flint-bearing  Chalk.  The  corals  are  not  usually  remarkable ;  reef- 
building  forms  may  be  found  in  the  lower  part  of  the  Cretaceous  in 
the  Northeastern  Alps ;  but  those  of  the  White  Chalk  are  small  and 
solitary.  Crinoids  and  starfishes  are  not  generally  abundant,  but 
echinoids  are  often  numerous,  and  the  irregular  group  is  more 
largely  developed  than  the  regular  one ;  in  the  Chalk  the  genera 
Echinoconus,  Echinocorys,  and  Micraster  are  common.*  The  poly- 
zoa  are  many.  Among  the  brachiopods  the  genera  Tcrcbratula  and 
Rhynchonella  dominate,  and  are  often  very  abundant.  Some  aber- 
rant bivalves  are  the  most  interesting  mollusca.  One  group  consists 
of  twisted  forms  allied  to  the  living  Chama,  and  to  the  older  genus, 
casts  of  which  present  a  rude  resemblance  to  a  pair  of  ram's  horns 
(Diceras) ;  in  the  other,  a  separate  family,  one  valve  is  funnel- 
shaped,  the  other  being  like  a  lid.  These  are  mainly  Cretaceous, 
but  are  rather  uncommon  in  England,  though  one  genus  (Radiolites] 
is  not  rare  at  the  base  of  the  Chalk  in  Cambridgeshire,  and  some- 
times attains  a  length  of  full  half  a  yard.f  Another  (Hippnritcs), 
also  large,  is  very  common  in  the  limestones  of  Southwestern 
FranCe.  Belemnites  are  less  abundant  than  formerly,  and  are 
chiefly  represented  by  a  sub-genus,  Bclemnitclla,  which  is  dis- 

*  The  commonest  species  are  Echinoconus  conicus  (Galerites  albogalerus),  Echinocorys 
•vulgaris  (Ananchyles  ovatus),  and  Micraster  coranguinum. 

f  Found  in  a  stratum  about  a  foot  thick,  rich  in  phosphatic  nodules,  called  the  Cam- 
bridge Greensancl,  which  is  about  the  age  of  the  very  top  of  the  Upper  Greensand,  and 
contains  many  fossils  washed  out  of  the  Gault, 


A    SKETCH  OF    THE   EARTH'S  LIFE-HISTORY. 


465 


tinguished  by  a  slit  on  the  side  of  the  "guard."  Ammonites  are 
still  fairly  common,  and  the  allied  forms,  which  no  longer  coil  them- 
selves in  a  plane-spiral,  are  much  more  abundant  than  they  were  in 
earlier  times.  The  Crustacea  approximate  more  closely  to  the 
types  of  succeeding  periods,  and  the  little  Cypris  with  allied  genera 
again  swarm  in  the  fresh-water  shales  of  the  Wealden. 

Among   the    vertebrates  the   "  bony  fishes "   assume   a   greater 


FIG.  161.— CRETACEOUS  FOSSILS. 


(i)   Hamites  attenuatus ;    (2)    Scaphites   ivanii ;  (3)    Ancyloceras  matherontanus  ;  (.4)     Turrilitei 
bergeri;  (5)  Baculites  anceps  ;    (6)  Ammonites  (Acanthoceras)  rothomagensis ;  (7) 
cornuvaccinum  ;  (8)  Belemnitella  mucronata. 


importance,  but  large  sharks,  armed  with  formidable  teeth,  must 
have  been  common  in  the  seas.  As  representatives  of  the  Reptiles, 
Ichthyosaurus  and  Plcsiosaurus  continue,  and  the  place  of  the  for- 
midable Pliosaurus  is  occupied  by  the  no  less  formidable  Polyptyclio- 
don.  The  winged-lizards  also  are  well  represented,  and  attain  on  the 
whole  to  a  larger  size  than  in  the  Jurassic  deposits,  for  here 
specimens  with  a  span  of  wings  amounting  to  as  much  as  twenty- 
five  feet  have  been  found.*  Chelonians  were  common  in  marshes, 
rivers,  and  seas,  as  well  as  crocodiles,  and  among  the  more  peculiar 
of  the  Cretaceous  reptiles  were  the  gigantic  snake-like  Pythono- 

*  Nicholson  and  Lydekker,  "  Manual  of  Palaeontology,"  p.  I2OI. 


466  THE   STORY  OF  OUR  PLANET. 

morpha.  One  genus,  Mosasaurus,  has  been  long  known  from  the 
magnificent  jaw  discovered,  in  1770  at  Maestricht,  in  a  yellow  lime- 
stone which  overlies  the  White  Chalk.*  A  number  of  extraordinary 
and  huge  creatures  belonging  to  the  same  order  have  been  unearthed 
in  Western  North  America,  and  reconstructed  by  Professor  Cope 
and  Professor  Marsh.f  Some  were  of  huge  size,  one  species  attain- 
ing a  length  of  seventy  feet.  The  sea  serpent  of  modern  times  is 
most  probably  a  myth  ;  in  the  Cretaceous  waters  it  was  a  reality. 

The  Dinosaurs  still  remain  as  "  lords  of  creation."  The  pre- 
daceous  Megalosaurus  continues  to  flourish,  but  is  joined  by  a 
creature  somewhat  similar  in  general  form,  but  which  must  have 
been  harmless,  for  it  was  an  herbivorous  animal — provided  it  did 
not  lose  its  temper,  when  it  could  have  made  itself  as  objectionable 
as  an  hippopotamus  or  rhinoceros.  This  was  the  Iguanodon,  first 
discovered  in  the  sandstones  of  the  Wealden  in  Sussex  by  the  late 
Dr.  Mantell,  which  was  for  some  years  a  sore  puzzle  to  the  compara- 
tive anatomist  of  the  last  generation.  For  a  considerable  time  the 
remains  discovered  were  in  a  very  fragmentary  condition,  but  at  the 
present  probably  no  dinosaur  is  better  known — at  any  rate,  in 
Europe.  This  has  been  the  result  of  a  most  singular  discovery 
made  in  1878  "in  the  colliery  of  Bernissart,  in  Belgium,  between 
Mons  and  Tournai,  near  the  French  frontier.  The  coal-bearing 
rocks  (Coal  Measures)  of  this  colliery,  overlain  by  Chalk  and  other 
deposits  of  later  age,  are  fissured  in  many  places  by  deep  valleys  or 
chasms  more  than  218  yards  deep.  Though  now  filled  up,  they 
must  at  one  time  have  been  open  gorges  on  an  old  land  surface. 
Into  one  of  these  chasms  were  somehow  precipitated  [twenty-nine] 
iguanodons,  numbers  of  fish,  a  frog-like  animal,  several  species  of 
turtles,  crocodiles,  and  numerous  ferns  similar  to  those  described  by 
Mantell  from  the  Weald. "^  At  least  five  of  these  iguanodons  are 
already  separated  from  the  matrix,  pieced  together,  and  exhibited  in 
the  museum  at  Brussels.  The  carcasses  may  have  been  swept  down 
by  floods,  which  are  sometimes  very  destructive  in  the  narrow 
ravines  of  districts  liable  to  sudden  and  heavy  rains ;  or  they  may 

*  The  specimen  is  now  at  Paris.  An  ecclesiastical  corporation  took  it  from  the  original 
discoverer  under  the  form  of  law,  and  a  French  army  took  it  from  them  by  the  right  of 
war ;  so  that,  on  the  whole,  justice  was  done,  except  to  the  original  discoverer,  who  got 
nothing  but  a  lawsuit  for  his  pains. 

f  Three  forms  are  depicted  in  Plate  XIII.  of  Mr.  H.  N.  Hutchinson's  book,  "  Extinct 
Monsters." 

\  H.  N.  Hutchinson's  "Extinct  Monsters,"  p.  91. 


A    SKETCH  OF    THE  EARTH'S  LIFE-HISTORY. 


467 


been  mired  if  a  boggy  spot  occurred  unexpectedly  at  this  place. 
The  creature,  as  already  said,  was  herbivorous,  sat  up  on  its  hind 
legs,  and  perhaps  progressed  somewhat  like  a  kangaroo ;  and  the 
larger  species  (for  there  are  two)  "measured  rather  more  than  thirty 
feet  from  the  tip  of  the  snout  to  the  end  of  the  tail,  and  could 
probably  lift  its  head  about  half  as  many  feet  above  the  ground. 

Hylceosaurns,  so  named  by  its  discoverer,  Dr.  Mantell,  because  it 
was  found  at  Tilgate  forest  on  the  Weald  of  Sussex,  took  the  place  of 
Scclidosaurus,  and  was  possessed  of  an  even  better  developed  dermal 

armature.  But  the  strangest 
creature  of  the  Cretaceous 
period  is  the  Triceratops  (three- 
horn  face)  of  America.  It  is 
one  of  the  latest  in  date  of  the 
Dinosauria,  for  its  remains  are 
found  in  the  Laramie  beds, 
which,  as  already  said  (p.  329), 
occupy  an  intermediate  position 
between  the  true  Cretaceous  and 
the  true  Eocene.  The  creature 


FIG.  162. — SKELETON  OF  IGUANODON. 

when  full  grown  was  probably  about  twenty-five  feet  long,  and  the 
top  of  its  back  was  full  eleven  feet  from  the  ground.  The  skull  was 
enormous — perhaps  quite  seven  feet  long,  and  of  an  extraordinary 
shape.  Above  the  nose  was  a  small  horn,  and  a  much  larger  one 
immediately  over  each  eye;  "the  back  part  of  the  skull  rises  up 
into  a  kind  of  huge  crest,  and  this  during  life  was  protected  by  a 
special  fringe  of  bony  plates."  The  mouth  terminated  in  a  kind  of 
beak  sheathed  with  horn,  and  the  creature  was  probably  provided 
with  some  sort  of  dermal  armor.  It  cannot  have  been  very  intelli- 
gent, for  "  the  brain  was  smaller  in  proportion  to  the  skull  than  any 
known  vertebrate."  Professor  Marsh  thinks  that  "  as  the  head  in- 
creased in  size  to  bear  its  armor  of  bony  plates,  the  neck  first,  then 


468  THE   STORY  OF  OUR  PLANET. 

the  fore  feet,  and  then  the  whole  skeleton  was  specially  modified 
to  support  it " ;  but  that  at  last  the  head  became  too  heavy  for  the 
body  to  bear,  and  led  to  the  extinction  of  the  race ;  so  that  the 
epitaph  on  Triceratops  might  be :  "I  and  my  race  died  of  over- 
specialization."* 

No  Cretaceous  mammals  have  yet  been  described,  though  they 
have  been  recently  found  in  America,  and  a  tooth  from  the  English 
Wealden  is  referred  by  Mr.  Lydekker  to  this  class.  Doubtless  they 
existed,  but  evidently  were  not  yet  important.  Some  scanty  re- 
mains of  birds  have  been  described  by  Professor  H.  G.  Seeley  from 
the  base  of  the  Chalk  of  Cambridgeshire ;  but  others,  in  better 
preservation  from  North  America,  have  been  the  subject  of  a 
memoir  by  Professor  Marsh.  He  describes  twenty  forms,  and  two 
of  the  genera  are  known  to  have  been  dentigerous.  One  Ichthy- 
ornis  (fish-bird),  with  well-developed  wings,  was  about  as  big  as  a 
rock  pigeon  ;  the  other,  Hesperornis  (bird  of  the  West),  may  have 
stood  five  or  six  feet  high.  It  was  unable  to  fly,  and  is  compared 
by  Professor  Marsh  to  a  swimming  ostrich. 

We  conclude,  then,  that  the  Secondary  era  witnessed  the  begin- 
ning of  Avian  and  Mammalian  life,  but  that  neither  class  was  able  to 
attain  to  importance.  They  appear  to  have  been  few  in  number, 
generally  small  in  size,  and  lowly  in  development.  It  was,  as  it  has 
been  often  called,  "  The  Age  of  Reptiles,"  characterized  by  their 
abundance,  magnitude,  and  variety.  They  filled  the  place  of  the 
whales  and  dolphins  in  the  seas,  of  the  herbivorous  and  carnivorous 
mammals  on  the  land,  of  the  vultures  and  cormorants  in  the  air. 
They  are  unimportant,  almost  unknown,  until  the  date  of  its  earliest 
deposits  ;  after  this  they  rapidly  rise  to  importance  ;  they  sink  into 
insignificance,  with  curious  abruptness,  at  its  close.  The  inverte- 
brates, however,  gradually  present  a  closer  resemblance  to  the  forms 
which  yet  exist.  Not  a  few  genera  which  still  survive  make  their 
appearance  in  the  Secondary  era ;  but,  as  a  rule,  those  which  are 
now  common  were  not  very  abundant  then,  while  those  which  were 
important  then  are  now  either  extinct  or  comparatively  rare.  This 
is  generally  true  of  the  corals,  the  echinoids,  and  the  mollusks,  and 
the  most  striking  fact  connected  with  the  last  is  the  extraordinary 
development  of  the  Belemnites  and  of  the  Ammonites,  and  their 
allies.  These  seem  to  run  parallel  with  the  peculiar  reptiles,  and 
they  disappear  as  completely  at  the  close  of  the  era. 

*  H.  N,  Hutchinson's  "  Extinct  Monsters,"  p.  107. 


A    SKETCH   OF    THE  EARTH'S  LIFE-HISTORY.  469 

The  fauna  of  the  Tertiary  era  differs  from  that  of  the  Secondary 
to  a  remarkable  and,  in  some  important  respects,  still  unaccount- 
able extent.  Hardly  a  single  species  of  the  one  era  survives  in 
the  other,  except  in  the  case  of  some  of  the  lowest  organisms, 
where  it  is  often  difficult  to  fix  the  limits  of  a  species,  or,  in  other 
words,  each  type  seems  somewhat  protean.  In  Britain  the  break 
between  the  two  series  is  very  great ;  in  Northwestern  Europe,  as 
already  said  (p.  41 2),  some  rather  scattered  and  fragmentary  deposits 
help  slightly  in  bridging  the  interval.  In  the  Yellow  Limestone, 
which  at  Meudon,  near  Paris,  at  Maestricht,  and  in  the  island  of 
Faxoe,  rests  unconf  ormably  upon  the  White  Chalk,  genera  belonging 
to  the  Cretaceous  system  are  found  associated  with  others  character- 
istic of  the  Eocene  ;  but  the  stratigraphical  break  disappears  farther 
away  to  the  southeast,  in  the  area  nearer  to  the  Mediterranean  Sea, 
where,  however,  fossils  are  generally  rather  scanty ;  while  in  the 
central  and  western  regions  of  North  America  the  transition  from 
the  Secondary  to  the  Tertiary  is  stratigraphically  complete.  The 
Laramie  beds  (p.  329),  which  attain  a  thickness  of  some  four  thou- 
sand feet,  if  the  flora  alone  were  considered,  would  be  regarded  as 
Tertiary,  but  their  fauna  is  more  closely  related  to  the  Secondary. 
They  contain  some  of  the  huge  reptiles  just  mentioned,  and  certain 
of  the  characteristic  Cretaceous  genera  of  cephalopods,  associated 
with  other  mollusks  which  are  more  distinctly  Eocene.  But  the 
greatest  puzzle  is  the  comparatively  rapid  disappearance  of  the 
huge  reptiles  and  their  replacement  by  hardly  less  huge  mammals. 
This,  no  doubt,  may  be  partly  explained  by  the  fact  that  our  idea 
of  the  later  Secondary  fauna  is  mainly  gathered  from  strata  which 
are  distinctly  marine,  while  the  Laramie  and  earlier  Eocene  beds, 
when  not  actually  fresh-water,  are  the  deposits  of  shallow  seas. 
This,  however,  by  no  means  solves  the  difficulty.  Some  of  the 
large  reptiles  of  the  Cretaceous  period  were  either  terrestrial  or 
amphibious,  living  under  conditions  similar  to  the  crocodiles,  alliga- 
tors, tortoises,  and  turtles  of  the  present  day.  If,  then,  representa- 
tives of  the  latter  reptiles  are  found  (and  by  no  means  rarely)  on 
both  sides  of  the  gap,  why  were  not  the  dinosaurs  able  to  cross  it, 
and  what  part  of  the  world  witnessed  the  development  of  the  large 
mammals  which  so  quickly  replaced  them  ?  These  appear  upon  the 
scene  like  adults,  like  the  first  colonists  of  a  new  region,  and  we 
cannot  find  their  nursery  or  their  schoolhouse.  Time  may  solve 
the  riddle,  future  discovery  may  bring  to  light  the  "  decline  and 
fall "  of  the  big  reptiles  and  the  contemporaneous  rise  of  the  big 


470  THE   STORY  OF  OUR  PLANET. 

mammals.  In  most  of  the  regions  hitherto  examined  this  transi- 
tional period  from  the  older  to  the  newer  era  was  evidently  one  of 
very  considerable  geographical,  and  probably  also  of  climatal, 
change.  Such  a  period  would  be  likely  to  produce  a  correspond- 
ing effect  upon  the  fauna,  to  be  rapidly  destructive  to  races  accus- 
tomed to  the  old  conditions — races  which  were  the  Bourbons  of 
the  animal  kingdom,  and  could  -neither  learn  nor  forget — and  to 
develop  with  comparative  rapidity  those  which  were  still  plastic 
and  capable  of  responding  to  stimulus.  There  may  be  to  a  species 
or  a  genus  a  time  of  senility  and  a  time  of  adolescence,  just  as  there 
is  to  an  individual.  It  is  obvious  that  in  the  Tertiary  era  the 
mammalia,  as  Professor  Gaudry  has  remarked,  were  in  the  full  swing 
of  their  evolution  (en  pleine  evolution}.  Still  the  comparative  sud- 
denness of  their  appearance  and  of  the  disappearance  of  the  great 
reptiles  are  facts — especially  the  former — which  in  the  present 
state  of  our  knowledge  make  a  point  for  the  advocate  of  special 
creation  and  are  a  difficulty  to  the  evolutionist. 

As  the  invertebrate  fauna  during  the  Tertiary  era  gradually  ap- 
proaches to  its  present  condition,  we  need  not  enter  into  the  details 
of  the  changes.  Only  a  small  number  of  the  genera  which  existed 
at  the  outset  have  since  become  extinct,  and  the  additions  in  this 
respect  have  not  been  large.  The  changes  are  chiefly  in  regard  to 
species.  According  to  Sir  C.  Lyell  the  percentage*  of  living  species 
in  the  mollusca  of  the  earlier  Eocene  deposits  amounted  to  about 
3^  per  cent.;  it  rose  in  the  Miocene  to  about  17  per  cent., attained 
to  from  35  to  50  per  cent,  in  the  older  Pliocene,  and  became  as  high 
as  from  90  to  95  per  cent,  in  the  newer  Pliocene.  These  figures  will 
give  a  rough  idea  of  the  gradual  change.  The  most  interesting  sig- 
nificance of  the  invertebrate  fauna — and  this  is  corroborated,  as 
already  said,  by  the  flora — is  the  evidence  which  it  bears  of  very 
marked  climatal  changes,  especially  in  the  northern  hemisphere.  A 
glance  at  a  collection  of  fossil  shells  from  the  London  Clay,  the  Brack- 
lesham,  or  the  Barton  beds  of  England,  indicates,  to  anyone  familiar 
with  the  present  distribution  of  mollusks,  the  presence — nay,  the 
marked  predominance — of  genera  characteristic  of  tropical  or  sub- 

*It  was  published  in  1833.  (See  "  Elements  of  Geology,"  ch.  xiii.  ed.  1865.)  Sub- 
sequent researches  have  shown  that  the  percentages  cannot  be  regarded  as  very  exact,  and 
they  are  liable  to  local  modification  ;  at  the  same  time  they  serve  better  than  anything 
else  to  give  a  general  idea  of  the  progressive  change  toward  the  present  condition  of 
things.  They  would  probably  be  roughly  true  for  the  invertebrates  generally,  but  in  the 
higher  vertebrates  the  change  is  more  striking,  for  a  large  number  of  genera  have  vanished, 
and  existing  species  make  a  comparatively  late  appearance. 


A    SKETCH  OF   THE  EARTH'S  LIFE-HISTORY.  471 

tropical  regions.  The  earliest  Tertiary  deposit  indicates  a  climate 
warmer  than  is  now  enjoyed  by  the  corresponding  locality — the 
temperature  probably  reached  its  highest  when  the  Bracklesham 
beds  were  deposited,  and  then  very  slowly  declined.  Still,  even  in 
Miocene  times,  the  climate  all  over  Europe,  and  probably  in  all 
parts  of  the  northern  hemisphere,  was  more  genial  than  at  present. 
If  we  are  permitted  to  fix  one  eye  on  the  present  age,  and  apply  a 
geological  telescope  to  the  other,  oleanders  then  might  have  been 
as  gay  in  the  parks  of  London  as  they  now  are  in  the  shrubberies  of 
the  Riviera ;  and  oranges,  with  their  golden  fruit,  as  in  the  streets 
of  Spezzia,  might  have  replaced  the  horse-chestnut  or  the  plane  in 
London  suburbs.  A  gradual  change  in  the  same  direction  was  in 
process  all  through  Pliocene  times,  until  at  last  an  extreme  of  cold 
was  reached  as  abnormal  as  the  warmth  had  been,  so  that  the 
musk-sheep  found  a  congenial  climate  in  the  valley  of  the  Thames. 
From  these  arctic  conditions  there  seems  to  have  been  a  gradual 
change  to  those  under  which  we  live.  It  is,  then,  obvious  that, 
though  the  English  climate  is  not  beyond  criticism,  it  has  been 
worse. 

Turning  to  the  higher  vertebrates,  we  find  that  both  birds  and 
mammals  exhibit  similar  changes,  but  the  remains  of  the  former 
at  present  discovered  are  so  much  more  scanty  that  it  may  suffice 
to  say  that  one  or  two  of  the  older  Eocene  forms,  like  those  men- 
tioned above,  were  dentigerous.*  Existing  genera,  as  a  rule,  cannot 
be  recognized  till  Miocene  times,  and  even  then  the  correspondence 
is  not  very  precise.  In  regard  to  the  mammals  much  fuller  in- 
formation has  been  obtained,  but  the  British  deposits,  owing  to 
local  circumstances,  have  not  supplied  important  contributions  to 
knowledge  till  the  later  part  of  the  Tertiary.  For  the  older  mam- 
malia, so  far  as  the  world  has  been  hitherto  examined,  it  is  neces- 
sary to  have  recourse  to  the  American  continent,  and  especially  to 
the  western  region  of  the  United  States.  There,  on  the  high  pla- 
teaus west  of  the  Rocky  Mountains,  in  Southern  Wyoming  and  in 
the  adjacent  parts  of  Utah  and  Colorado,  is  a  thick  group  of 
deposits  of  lacustrine  origin,f  from  which  a  great  number  of  mam- 
malian remains  have  been  disinterred,  which  have  been  studied  in 

*  The  projections  on  the  bill,  however,  are  not  teeth  in  so  strict  a  sense  as  in  the  Sec- 
ondary birds. 

f  According  to  Professor  Marsh  the  vertical  thickness  of  these  deposits  exceeds  a  mile. 
The  district,  now  from  6000  to  8000  feet  above  sea  level,  is  drained  by  the  Green  River, 
the  principal  tributary  of  the  Colorado. 


47*  THE   STORY  OF  OUR  PLANET. 

detail  by  Professors  Marsh,  Cope,  and  others.  The  creatures  thus 
reconstituted  are  hardly  less  strange  than  the  Secondary  reptiles, 
which  have  been  discovered  in  the  same  part  of  the  continent. 
Truly  America  is  the  parent  of  prodigies,  for  its  physical  features 
and  its  palaeontological  products  are  alike  on  a  grandiose  scale.  The 
shores  of  this  lake  were  haunted  by  a  strange  group  of  monstrous 
beasts,  which  cannot  be  fitted  exactly  into  any  existing  order. 
They  are  placed  in  that  of  the  Dinocerata,  or  "  fearsome-horned  " 
mammals,  because  of  certain  protuberances  on  the  skull,  which  sug- 
gest the  presence  of  horns  or  organs  of  that  nature.  Taking  as  an 
example  one  of  these,  named  Dinoceras  ingens,  we  find  that  in  the 
body  it  was  something  like  an  elephant,  its  head  roughly  resembled 
that  of  a  two-horned  rhinoceros,  but  it  had  besides  two  protuber- 
ances of  smaller  size,  just  above  the  nose,  and  two  others,  quite  as 
long  as  the  "  nose  horns,"  but  rather  blunter  in  form,  above  the  ears. 
All  these  are  actual  bony  protuberances  on  the  skull,*  and  their 
external  appearance  is  a  matter  of  conjecture.  Also  the  two  canine 
teeth  of  the  upper  jaw  were  greatly  elongated,  especially  in  the  male. 
The  creature  was  about  twelve  feet  long,  not  reckoning  the  tail. 
These  Dinocerata,  according  to  Professor  Marsh,  have  been  found 
as  yet  only  about  the  Wyoming  lake  basin,  none  being  known 
from  any  other  part  of  America  or  from  the  Old  World.  Numer- 
ous other  mammals  are  found,  not  only  in  the  New  World  but  also 
in  the  Old,  in  strata  of  Eocene  and  Oligocene  age.  Deposits  now 
classed  with  the  latter  have  given  up  several  forms,  both  in  the  Isle 
of  Wight  and  still  more  in  the  Paris  basin.  These,  however,  do  not 
reach  the  gigantic  size  of  the  Dinocerata,  but  vary,  like  the  ordinary 
European  mammals  of  the  present  day,  from  the  size  of  a  large 
stag  downward.  It  is  difficult  to  class  them  with  any  of  the 
existing  orders  for  the  reason  already  mentioned.  Some  present 
resemblances  to  tapirs,  some  to  deer,  some  to  pigs,  some  dimly  fore- 
shadow the  horse,  others  might  even  claim  a  connection  with  the 
rhinoceros. 

In  the  Miocene  period  the  relationship  to  existing  mammals 
becomes  more  strongly  marked.  North  America  still  takes  the  lead 
in  monsters,  which  come  from  the  remains  of  an  old  lake  basin,  this 
time  east  instead  of  west  of  the  Rocky  Mountains,  and  near  the 
present  head-waters  of  the  Missouri.  This  district  was  the  principal 
resort  of  Brontops  (thunder-face),  a  creature  something  like  a  rhi- 

*  This  is  not  the  case  with  the  "  horn  "  of  the  rhinoceros. 


A    SKETCH  OF    THE  EARTH'S  LIFE-HISTORY.  473 

noceros,  but  with  a  pair  of  bony  prominences  above  the  nostrils. 
The  head  and  neck  were  both  longer  in  proportion  than  in  that 
animal,  the  former  being  broad  and  shallow.  Brontops  was  about 
twelve  feet  long,  without  the  tail,  and  eight  feet  high.  But  though 
many  strange  forms  continue  to  recall  the  older  Tertiary  mammals, 
we  begin  in  the  Miocene  to  meet  with  the  ancestors,  as  they  may 
be  called,  of  families  which  still  exist,  both  in  the  New  World  and 
in  the  Old.  Marsupials  were  then  much  more  widely  distributed 
than  now.  Edentates  (such  as  the  sloths,  armadillos,  and  ant- 
eaters)  occur  on  both  sides  the  Atlantic,  and  their  representatives 
in  the  southern  parts  of  Europe  reached  a  large  size.  Cetaceans, 
allied  to  whales,  seals,  and  sirens,  make  their  appearance  ;  beasts  are 
found  more  closely  allied  to  horses  and  deer,  to  the  elephant,  the 
rhinoceros,  and  the  hippopotamus.  In  fact,  the  ungulate  or  hoofed 
quadrupeds  are  very  numerous  in  the  Miocene.  The  carnivora  have 
hardly  attained  to  their  present  importance ;  but  the  remains  of 
simians,  the  family  most  closely  related  to  man,  have  been  dis- 
covered. One  (Dryopithecus),  from  Miocene  deposits  in  France  and 
Hesse-Darmstadt,  was  an  ape  about  as  big  as  a  chimpanzee,  with 
teeth  resembling  those  of  the  gorilla.  In  England  the  Miocene 
record  is  a  total  blank,  but  the  Pliocene  deposits,  though  of  no 
great  thickness,  have  yielded  a  fair  supply  of  mammals.  These 
have  been  largely  augmented  from  the  region  bordering  the  Medi- 
terranean, and  yet  more  remarkably  by  the  deposits  of  the  Siwalik 
Hills  in  India.  For  this  period  the  New  World  supplies  less  infor- 
mation than  the  Old.  Among  the  most  remarkable  forms  of 
Pliocene  age  were  the  giant  tortoise  of  Northern  India,  the  shell  of 
which  was  not  less  than  a  couple  of  yards  long,  about  double  the 
length  of  the  biggest  now  in  existence,  and  the  Sivatherium  (beast 
of  Siva),  a  ruminant  bigger  than  any  now  living,  for  it  was  larger 
than  a  rhinoceros;  this  bore  two  pairs  of  horns,  and  seems  in  some 
respects  intermediate  between  the  giraffes  and  the  antelopes.  But 
in  the  Pliocene  deposits,  particularly  in  the  upper  portion,  genera 
either  still  living  or  differing  from  these  but  little  become  common. 
The  rhinoceros,  the  elephant,  the  hippopotamus,  the  horse,  the  bear, 
the  hyena,  the  lion,  are  all  in  existence.  In  Europe  alone  there  were 
at  least  as  many  species  of  rhinoceros,  and  more  than  as  many  of 
elephants,  as  there  are  now  in  the  world.  The  great  mastodons — 
creatures  allied  to  the  elephant — and  the  saber-toothed  tiger 
{Maclicerodus)  must  not  be  forgotten.  This  also  is  worthy  of 
notice.  Excluding  a  few  forms  most  common  in  the  extreme  north 


474  THE  STORY  OF  OUR  PLANET. 

of  the  two  hemispheres,  we  find  that  a  marked  separation  now  exists 
between  the  mammals  of  the  Old  and  the  New  World.  In  Pliocene 
times  it  was  not  so  ;  a  horse,  a  mastodon,  an  elephant,  a  rhinoceros, 
a  tiger,  a  camel,  not  to  mention  others,  formed  strong  connecting 
links  between  the  two  hemispheres.  Professor  Dana  remarks  on 
the  animals  which  lived  in  the  Upper  Missouri  region  that  "  the 
collection  has  a  strikingly  Oriental  character,  except  in  the  prepon- 
derance of  herbivores."  * 

The  post-Tertiary  or  Pleistocene  does  not  require  a  long  notice. 
In  the  earlier  part  of  this  period,  if  it  may  be  so  designated,  a 
remarkably  low  temperature  prevailed  generally — at  any  rate,  in 
the  northern  hemisphere.  This  displaced,  and  no  doubt  to  some 
extent  modified,  the  fauna  and  flora,  but  it  does  not  seem  to  have 
effected  any  great  destruction  of  species,  and  the  chief  change  since 
that  time  has  been  the  gradual  disappearance  of  sundry  of  the 
larger  mammalia,  due  probably  in  no  small  part,  directly  or  indirectly, 
to  the  action  of  man.  It  may  suffice,  so  far  as  the  Old  World  is 
concerned,  to  indicate  in  a  very  few  words  the  condition  of  our  own 
land  at  a  time  when  the  Glacial  epoch  was  passing  away,  and  the 
climate  gradually  became  less  severe. 

Britain  at  this  time,  as  already  mentioned,  formed  part  of  the 
continent  of  Europe,  the  North  Sea,  the  English  Channel,  St. 
George's  Channel  being  then  dry  land.  Northwestern  Europe, 
thus  enlarged,  exhibits  a  goodly  list  of  large  animals.  Among 
them  are  two  species  of  elephant ;  the  one,  Elcphas  antiquus,  which 
more  closely  resembles  the  African  elephant,  may  have  been  only  a 
summer  visitant  to  this  country,  in  company  with  the  hippopotamus; 
but  the  other,  the  mammoth,  was  a  permanent  resident,  for  it  was 
protected  by  its  woolly  covering  against  all  inclemencies  of  climate. 
There  were  also  two  species  of  rhinoceros,  one  of  them  being  similarly 
clothed.  Lions  must  have  been  as  abundant  in  the  lowlands  round 
the  Mendips  as  they  were  in  the  wilder  parts  of  Southern  Africa  at 
the  beginning  of  this  century;  the  caves  in  many  parts  of  England 
were  the  dens  of  hyenas ;  bears  also  were  plentiful.  Food  for  the 
predatory  animals  was  not  lacking ;  the  broad  lowlands,  now  sea 
beds,  afforded  ample  pasture  to  droves  of  horses  and  herds  of  rein- 
deer and  red  deer;  and  besides  these  were  the  urus,  an  extinct 
species  of  ox,  and  the  Irish  elk,  also  extinct ;  the  bison,  lingering 
now  in  Lithuanian  forests,  but  then  as  common  in  Europe  as  till 

*  "  Manual  of  Geology,"  p.  508,  second  edition. 


A    SKETCH  OF  THE  EARTH'S  LIFE-HISTORY.  475 

lately  its  American  relative  was  on  that  continent,  while  the  wild 
boar  and  other  smaller  quadrupeds  need  not  be  mentioned.  The 
condition  of  Western  Europe  in  those  days  must  have  resembled,  so 
far  as  the  quadrupeds  are  concerned,  that  of  North  America  or  of 
Southern  Africa  before  the  gun  or  rifle  of  the  white  man  had 
replaced  the  spears  and  arrows  of  the  savage.  That  many  of  these 
creatures  were  hunted  by  man  is  a  certainty.  In  not  a  few  caves, 
notably  in  those  of  the  Dordogne,  the  debris  strewn  upon  the  floor, 
and  sometimes  the  rude  carvings  on  bone  and  horn,  show  that  the 
reindeer,  the  Irish  elk,  the  horse,  the  bison,  the  ibex,  the  musk- 
sheep,  etc.,  were  hunted  and  were  consumed  by  their  inmates. 
Even  the  mammoth  itself  may  have  been  a  victim  to  their  rudely 
chipped  spear  heads  of  flint,  for  its  bones  have  been  found,  and  a 


FIG.  163.— ENGRAVING  OF  MAMMOTH,  FROM  THE  DORDOGNE  CAVES  (REDUCED). 

fragment  of  a  tusk  bears  a  likeness  of  the  beast,  roughly  engraved, 
but  indubitable. 

More  marked  changes  in  mammalian  life  are  indicated  in  the 
southern  hemisphere.  In  South  America  the  fluviatile  deposits  of 
Pleistocene  age,  which  form  the  widespread  plains  of  Patagonia  and 
of  Brazil,  have  yielded  the  remains  of  gigantic  allies  of  the  sloths 
and  of  the  armadillos.  A  species  of  MegatJierium  (great-beast),  one 
of  the  best  known  of  the  former,  was  "  fully  equal  in  bulk  to  the 
largest  species  of  rhinoceros,"  while  Glyptodon  (sculptured-tooth), 
which  was  more  completely  sheathed  than  the  latter  animals,  was 
seven  feet  long  in  the  body. 

At  the  same  geological  epoch  Australia  possessed  mammals  of  a 
larger  size  than  at  present  are  found  within  its  limits.  The  latter, 
it  is  well  known,  represent  only  the  lowest  orders,  the  monotremes 
and  marsupials ;  and  a  study  of  fossils  indicates  that  in  earlier  times 
the  higher  orders  were  also  wanting  in  this  part  of  the  globe.  The 
predecessors,  however,  of  the  existing  wombats  and  kangaroos  some- 


47 6  THE   STORY  OF  OUR  PLANET. 

times  attained  to  a  great  size.  One  of  the  former  was  probably  as 
large  as  a  tapir  and  of  stouter  build  ;  another,  Diprotodon  (tvvo-f  ront- 
tooth),  the  representative  of  an  extinct  family,  was  much  bigger,  for 
it  was  equal  in  size  to  a  large  -rhinoceros ;  a  third,  intermediate  in 
zoological  characters  between  these  two,  but  about  the  size  of  the 
former,  is  supposed  to  have  been  a  burrowing  animal.  There  was 
also  a  predaceous  marsupial,  Thylacoleo  (pouch-lion),  as  big  as  a  lion. 
The  kangaroos  themselves  have  fossil  representatives,  some  of  large 
size.  In  New  Zealand,  as  is  well  known,  are  no  indigenous  mam- 
mals, and  none  have  been  found  fossil.  But  it  was  formerly  inhab- 
ited by  a  huge  and  remarkable  group  of  birds — the  moa  or  Dinor- 
nis  (terrible-bird) — still  represented  in  that  country  by  the  little 
Apteryx  or  kiwi.  This  also  seems  to  have  had  a  giant  predecessor, 
while  the  moas  were  often  much  bigger  than  the  largest  ostrich,  one 
species  standing  about  ten  feet  high.  They  were  quite  wingless, 
but  their  legs,  as  a  compensation,  were  remarkably  strong.  Some 
species  of  a  very  large  wingless  bird  (sEpyornis)  have  been  also 
found  in  Madagascar,  the  largest  of  which  rivaled  in  size  the  biggest 
New  Zealand  moa.  The  eggs  of  both  these  creatures  have  been 
discovered,  and  were  proportionately  large,  that  of  jBpyornis  being 
about  fourteen  inches  in  diameter.  The  moas  undoubtedly  sur- 
vived in  New  Zealand  till  a  comparatively  late  date,  and  were  killed 
off  by  the  natives ;  but  in  all  probability  some  time  before  the  arri- 
val of  the  first  English  settlers. 

Some  remarks  will  be  made  in  a  later  chapter  on  the  signifi- 
cance of  the  present  distribution  of  life  upon  the  globe,  and  the 
relations  of  past  and  present  forms.  Here  it  may  suffice  to  observe 
that  a  survey  of  palaeontology  leads  us  to  the  following  general 
conclusions: 

(1)  That  a  group  of  living  creatures,  assuming  its  cycle  to  be 
complete,  follows  a  course  analogous  to  that  of  an  individual.     It 
appears,  culminates,  declines,  and  disappears. 

(2)  That,  on  the  whole,  there  has  been  a  progressive  advance  in 
organization ;  the  work  of  life  in  the  world,  so  to  say,  as  time  ad- 
vances, is  done  by  more  highly  developed  creatures,  though  the 
"  children  of  Gibeon  "  yet  remain. 

(3)  That  the  earlier  types  are  commonly  of  a  more  generalized 
character  than  their  later  representatives,  according  better  with  the 
more  embryonic  stages  in  the  development  of  these,  and  frequently 
combining  characters  which  are  now  divided  among  distinct  groups. 

(4)  That,  in  the  various  quarters  of  the  globe,  ancestral  forms  of 


A    SKETCH  OF    THE  EARTH'S  LIFE-HISTORY.  477 

the  creatures  which  now  occupy  the  same  region  may  be  found  ; 
but  evidently  the  ancient  geographical  divisions  often  differed  much 
from  the  present,  and  indications  may  be  detected  of  the  existence 
of  communications  which  have  been  long  severed. 

(5)  That  in  past  times  signs  of  climatal  differences  are  exhibited 
which  have  affected  the  distribution  of  plants  and  animals,  and  can 
be  traced  back  for  at  least  a  considerable  distance  in  geological  his- 
tory, and  that  variations  of  climate  have  been  a  most  important 
factor  in  the  migration  and  distribution  of  species. 

(6)  That  though  a  species  seemingly  makes  its  appearance  and 
vanishes  abruptly,  this  is  not  a  safe  basis  for  inference,  owing  to  the 
known  imperfection  of  the  geological   record,   and  that  certainly 
there  is  not,  even  from  the  earliest  epoch,  the  slightest  evidence  of 
any  general  catastrophic  destruction  of  life  and  repeopling  of  the 
globe. 


PART  V. 
ON  SOME  THEORETICAL  QUESTIONS. 


CHAPTER  I. 

THE  AGE  OF  THE  EARTH. 

ONE  other  question  claims  attention  before  this  story  is  brought 
to  a  conclusion — namely,  What  is  the  earth's  age?  In  some  of  the 
preceding  chapters  the  operations  of  processes  destructive  and  con- 
structive have  been  indicated.  In  those  which  followed  the  forms 
of  living  creatures,  long  since  vanished,  were  sketched,  and  the  con- 
nection between  the  present  and  the  past  disposition  of  land  and 
water  has  been  established,  so  far  as  the  evidence  admits.  But 
these  changes,  this  evolution  alike  of  the  earth's  tenants  and  of  its 
physical  features,  require  time,  and  cannot  be  compressed  into  a 
few  decades  of  centuries.  Is  it,  then,  possible  to  express  this 
period,  however  approximately,  by  years,  and  to  compare,  however 
roughly,  the  duration  of  the  earth  with  the  life  of  man,  although, 
perhaps,  a  millennial  epoch  of  the  one  may  be  analogous  to  the  day 
of  the  other? 

A  solution  of  the  problem  might  be  attempted  by  approaching  it 
from  the  standpoint  of  the  geologist.  By  means  of  numerous  and 
careful  observations  an  estimate  might  be  formed,  on  the  one  hand, 
of  the  rate  at  which  rivers  lower  their  beds  and  seas  encroach  upon 
the  land;  on  the  other,  of  the  time  occupied  in  the  accumulation  of 
a  certain  amount  of  deposit,  whether  it  be  conglomerate  or  sand, 
fine  mud  or  calcareous  ooze.  The  thickness  also  of  the  different 
kinds  of  stratified  rock  might  be  ascertained,  and  then,  after  a  care- 
ful estimate  of  averages,  the  time  required  to  build  up  the  complete 
series  might  be  determined  by  a  sum  in  simple  proportion.  This, 
however,  at  best,  would  be  only  a  minimum  estimate,  for  it  would 
take  no  account  either  of  strata  which  had  been  removed  by  denu- 
dation, or  of  certain  metamorphic  rocks,  the  origin  of  which  is  often 
doubtful.  Great  difficulty  also  at  present  exists  in  deciding  what 
is  a  fair  estimate  for  the  thickness  of  the  stratified  rocks,  and,  lastly, 
the  validity  of  any  result  obtained  by  applying  the  "rule  of  three" 
to  geology  is  always  open  to  question.  Denudation  and  deposition 
proceed  at  such  different  rates  under  different  circumstances;  the 


482  THE   STORY  OF  OUR  PLANET. 

presence,  or  comparative  absence,  of  vegetation ;  the  character  of 
the  climate,  whether  equable  or  extreme,  and  many  like  disturbing 
causes,  produce  so  much  variation  that  it  becomes  extremely  diffi- 
cult to  strike  an  average.  We  may  steadfastly  decline  to  accept 
the  hypotheses  of  "convulsionists,"  and  yet  be  consistent  in  believ- 
ing that  epochs  of  comparative  unrest  and  of  comparative  calm  may 
have  alternated  in  one  and  the  same  part  of  the  globe,  and  that  a 
chronology,  founded  on  the  present  condition  of  any  region,  may 
be  easily  either  much  in  excess  or  much  in  defect  of  the  truth. 

Geologists,  influenced  strongly  by  the  dictum  of  Hutton  that  the 
earth  itself  showed  no  trace  of  a  beginning  or  sign  of  an  end,  had 
fallen,  not  many  years  since,  into  the  habit  of  regarding  past  time 
as  practically  boundless.  Like  a  young  man  who  has  come  into 
possession  of  the  wealth  accumulated  during  a  long  minority,  they 
appeared  to  deem  the  balance  at  their  disposal  inexhaustible,  and 
drew  checks  lavishly  on  the  bank  of  time.  But  just  as  a  friend 
with  wider  experience  might  act  the  mentor  to  the  spendthrift,  so 
the  physicist  has  uttered  more  than  one  warning  to  the  geologist. 
Of  these  one  is  founded  on  the  retardation  of  the  earth's  motion 
caused  by  the  tides.  It  may  be  stated  in  the  words  of  Professor 
G.  Darwin:*  "Since  water  is  not  frictionless,  tidal  oscillations  must 
be  subject  to  friction ;  ...  an  inevitable  result  of  this  friction  is 
that  the  diurnal  rotation  of  the  earth  must  be  slowly  retarded,  and 
that  we,  who  accept  the  earth  as  our  timekeeper,  must  accuse  the 
moon  of  a  secular  acceleration  of  her  motion  round  the  earth,  which 
cannot  be  otherwise  explained.  It  is  generally  admitted  by 
astronomers  that  there  actually  is  such  an  unexplained  secular 
acceleration  of  the  moon's  mean  motion."  If  this  secular  accelera- 
tion be  estimated  at  a  certain  amount,  "the  earth  must  in  a  century 
fall  behind  a  perfect  chronometer,  set  and  rated  at  the  beginning  of 
the  century,  by  twenty-two  seconds";  if  this  be  so,  "then  a  thou- 
sand million  years  ago  the  earth  was  rotating  twice  as  fast  as  at 
present."  But  if  it  solidified  either  at  that  or  an  earlier  epoch,  this 
increase  in  the  speed  of  rotation  would  impress  upon  the  earth  a 
form  more  distinctly  spheroidal  than  its  present  one;f  from  this  it 
may  be  inferred  that  solidification  occurred  at  a  much  less  remote 
period,  when  the  speed  of  rotation  corresponded  more  nearly  with 


*  Address  to  Section  "  A"  of  the  British  Association  at  the  Birmingham  meeting,  1886. 
f  That  is  to  say,  the  so-called  circles  of  longitude  would  be  more  distinctly  elliptical 
than  at  present. 


THE  AGE   OF   THE  EARTH.  483 

the  rate  of  to-day.  Moreover,  if  the  earth's  form  originally  were 
more  elliptical  than  at  present,  land  should  predominate  over  sea  in 
its  equatorial  regions ;  but  this,  as  has  been  already  shown,  is  far  from 
being  the  case.  But  to  this  remonstrance  the  geologist  replies  that 
the  effects  of  denudation  may  have  very  materially  altered  the  rela- 
tive position  of  sea  and  land  in  the  lapse  of  ages,  and  besides  this, 
the  present  form  of  the  earth  may  not  correspond  with  the  original 
one;  for  the  material  of  which  it  consists  may  not  be  absolutely 
rigid,  but  may  permit  of  its  form  being  slowly  adjusted  from  time 
to  time  to  correspond  with  the  rate  of  rotation.*  In  the  latter 
contention  the  geologist  would  find  that  some  physicists  would 
come  to  his  support. 

Another  warning  is  founded  on  the  secular  cooling  of  the  earth. 
Lord  Kelvin,  in  his  well-known  essayf  on  this  subject,  came  to  the 
conclusion  that  during  the  last  96,000,000  years  "the  rate  of  increase 
of  temperature  underground  has  gradually  diminished  from  about 
one-tenth  to  about  one-fiftieth  of  a  degree  Fahrenheit  per  foot." 
The  rate  of  cooling  thus  indicated  implies  that  in  all  probability 
not  more  than  100,000,000  of  years,  at  a  rough  estimate,  can  have 
elapsed  between  the  first  formation  of  a  solid  crust  on  the  globe 
and  the  present  condition  of  things.  But  here  also  Professor  Dar- 
win has  pointed  out  the  possibility  of  a  flaw  in  the  argument,  the 
result  of  which  would  be  a  lengthening  of  the  time.  But,  in  any 
case,  whether  this  extension  be  allowed  or  not,  whether  the  numeri- 
cal value  of  the  result  may  or  may  not  be  affected  by  the  imperfec- 
tions in  certain  data  on  which  it  depends,  the  main  contention  of 
the  physicist  holds  good — viz.,  that  there  must  be  a  limit,  and  this 
not  an  extraordinarily  distant  one,  to  geological  time.  Matters 
remained  in  this  position  till  Lord  Kelvin  again  startled  the  geolo- 
gists by  proposing  a  further  curtailment  of  geological  time  by  con- 
sidering the  problem  from  another  point  of  view.  Demur  if  you 
will,  he  seemed  to  say,  to  the  tidal  retardation  of  the  earth  and  to 
the  consequence  of  its  secular  cooling,  but  can  you  be  certain  about 
the  duration  of  the  sun?  However  long  the  earth  has  been  in  exist- 
ence, for  at  least  this  time  the  sun  must  have  been  radiating  heat 
into  space.  The  amount  can  be  estimated  with  some  accuracy. 
Suppose  it  should  be  discovered  that  in  the  time  which  you  geolo- 

*If  a  flexible  hoop  were  set  rotating  about  a  rod,  upon  which  its  upper  part  could  move 
freely  up  and  down,  its  form  would  become  lessor  more  circular  as  the  velocity  of  rotation 
increased  or  decreased. 

f  Republished  in  Thomson  and  Tail's  "  Natural  Philosophy,"  Appendix  D. 


484  THE   STORY  OF  OUR  PLANET. 

gists  demand,  the  light  would  have  faded  into  darkness  and  the 
central  fire  would  have  gone  out?  Lord  Kelvin  has  discussed  the 
problem  and  arrived  at  this  conclusion:  "It  seems,  therefore,  on 
the  whole  most  probable  that  the  sun  has  not  illuminated  the  earth 
for  100,000,000  years,  and  almost  certain  that  he  has  not  done  so 
for  500,000,000  years.  As  for  the  future,  we  may  say  with  equal 
certainty  that  inhabitants  of  the  earth  cannot  continue  to  enjoy 
the  light  and  heat  essential  to  their  life  for  .many  million  years 
longer,  unless  sources,  now  unknown  to  us,  are  prepared  in  the 
great  storehouse  of  creation."*  But  this  conclusion  also  is  not 
universally  accepted,  for  some  physicists  maintain  that  such  a 
source  is  even  now  in  operation,  and  that  the  sun's  heat  is  kept 
up— its  fires,  so  to  say,  are  fed— by  the  incessant  shower  of  meteor- 
ites which  is  rained  down  upon  it  from  celestial  space.  But  though 
this  process  of  "coaling  the  sun"  may  be  really  going  on,  though 
atom  after  atom  in  the  incessant  collisions  may  be  changed  from  a 
solid  to  a  vapor,  and  add  its  tiny  quota  of  energy  to  the  great  cen- 
tral storehouse,  there  is  no  proof  that  space  is  studded  so  thickly 
with  star  dust  as  to  compensate  for  the  lavish  expenditure  of  light 
and  heat.  Hence,  though  this  income  may  postpone  the  final  bank- 
ruptcy that  fate  seems  to  be  inevitable. 

Attempts,  indeed,  have  been  made,  still  in  connection  with  the 
duration  of  the  heat  of  the  sun,  to  restrict  the  geologist  within 
limits  still  more  narrow  than  those  just  named — to  allow  only  a 
very  few  millions  of  years  for  enacting  all  the  drama  of  life.  Here, 
however,  he  may  justly  make  a  stand.  If  he  has  been  obliged  to 
found  his  estimate  of  time  upon  uncertain  data,  the  physicist  also, 
as  has  been  said,  is  in  no  better  plight.  In  each  of  these  three 
pieces  of  mathematical  reasoning,  as  soon  as  any  attempt  is  made 
to  express  the  results  in  an  arithmetical  form,  assumptions  are 
introduced  which  cannot  be  regarded  as  beyond  question,  and  the 
geologist  is  justified  in  retorting  with  a  tu  quoque  on  the  physicist. 

We  come,  then,  to  the  conclusion,  on  a  review  of  the  whole  sub- 
ject, that  the  knowledge  at  present  available  is  insufficient  for  an 
accurate  solution  of  the  problem,  but  that,  on  the  one  hand,  the 
physicist  can  show  that  the  earth  and  its  order  had  a  beginning, 
and  that  this  must  fall  within  a  limit  of  time  which  would  have  been 
formerly  deemed  restricted — say,  as  a  rough  and  outside  approxima- 
tion, something  like  100,000,000  years — while,  on  the  other  hand, 

*  Thomson  and  Tail,  "  Natural  Philosophy,"  Appendix  E. 


THE  AGE   OF   THE  EARTH.  485 

the  geologist  can  show  that,  so  long  as  we  suppose  the  earth  to 
have  been  governed  by  laws  in  general  correspondence  with  those 
by  which  it  is  still  regulated,  the  history  of  the  stratified  rocks 
and  of  the  development  of  life  cannot  possibly  be  condensed  into 
some  twenty  or  thirty  million  years.  In  other  words,  we  may 
affirm  that  the  aeon  of  the  earth  is  long,  but  it  is  very  far  from 
being  boundless. 


CHAPTER  II. 

THE   PERMANENCE   OF   OCEAN   BASINS   AND   LAND   AREAS. 

WE  have  already  shown  that  the  changes  in  the  physical  geog- 
raphy of  the  globe  have  been  many  and  great,  so  that  the  same 
spot  on  its  surface  may  have  alternated  more  than  once  between 
land  and  sea.  This  is  universally  admitted  among  geologists.  But 
here  agreement  ceases.  Some  hold  that  our  continents  occupy  the 
sites  of  ocean  basins,  and  our  oceans  flow  deep  over  submerged 
continents;  while  others  maintain  that,  though  there  have  been 
many  oscillations  of  level,  each  large  mass  of  land  indicates  a 
region  which,  from  a  very  early  time  at  least,  has  been  more  or  less 
continental  in  character,  and  the  deeper  parts  of  the  ocean,  prob- 
ably, have  never  risen  above  the  surface.  This  question — the  per- 
manence of  ocean  basins,  as  it  is  called — is  one  which  is  no  less 
interesting  than  difficult.  The  evidence  upon  which  the  answer 
must  depend  is  mainly  indirect;  for,  obviously,  the  deep  sea  guards 
its  own  secrets.  We  may,  however,  observe  that  the  great  size  of 
the  hollows  of  the  ocean  compared  with  the  protuberances  of  the 
land  masses,  to  which  attention  has  already  been  called,*  makes  it 
probable  that  the  deeper  parts  of  the  basins  will.be  very  persistent 
features  of  the  earth's  crust.  But  some  inferences  may  be  drawn 
from  the  rocks  themselves,  and  some  from  the  present  distribution 
of  life  on  the  globe.  If  rocks  are  composed  of  ordinary  detrital 
materials,  such  as  thick  masses  of  sandstone  and  silty  clay,  it  may 
be  justifiably  assumed  that  they  were  deposited  at  no  great  distance 
from  a  considerable  land  area,  generally  at  most  not  much  more 
than  a  hundred  miles,  and  very  often  less.  Thus  the  building 
stones  of  the  British  Isles — and  the  same  statement  holds  good  of 
many  parts  of  Europe — prove  the  proximity  of  ancient  land  masses. 
Deposits,  however,  occur  at  intervals — such  as  the  Chalk  or  the 
Carboniferous  limestone,  which  are  conspicuously  free  from  detrital 
material,  and  almost  wholly  composed  of  the  dtbris  of  organisms.f 
But  this  does  not  necessarily  prove  that  the  water  was  deep — only 

*  Pp.  12,  59.  f  See  pp.  384,  449. 


PERMANENCE   OF  OCEAN  BASINS  AND  LAND  AREAS.        487 

that  it  was  clean.*  The  organisms  of  the  Carboniferous  limestone 
are  so  slightly  related  to  living  forms  that  they  are  of  little  avail  for 
inductive  reasoning  as  to  their  probable  environment ;  but  those  of 
the  chalk,  in  the  opinion  of  zoologists,  do  not  indicate  very  deep 
water.  At  present,  abyssal  depositsf  have  not  been  generally 
recognized  among  continental  rocks.  No  great  stress,  however,  can 
be  laid  upon  this  negative  evidence,  because  we  have  so  little 
knowledge  of  what  the  very  deep-sea  deposits  of  ancient  days  would 
be  like.  A  foraminiferal  ooze  would  awaken  suspicions,  but  it 
would  not  be  conclusive,  because  many  foraminifera  live  close  to 
the  surface;  a  radiolarian  ooze  would  do  this  still  more,  because 
they  can  also  live  at  a  great  depth,  and  their  "tests"  endure, 
whereas  calcareous  organisms  are  destroyed ;  a  very  fine,  almost 
impalpable  mud,  which  resembled  a  chemical  precipitate  rather 
than  a  detrital  deposit,  would  be  most  of  all  suggestive;  but  to 
diagnose  such  a  rock  under  the  microscope  would  be,  obviously,  no 
easy  task.  Hence  we  cannot  venture  to  say  much  more  than  that 
the  constituent  rocks  of  continents,  while  they  undoubtedly  give 
proofs  of  considerable  oscillations,  testify  frequently  to  the  prox- 
imity of  ancient  land,  and  rarely,  if  ever,  demonstrate  abyssal  con- 
ditions.^: 

But  the  comparative  study  of  the  faunas  and  floras  of  different 
regions  seems  to  throw  some  light  on  the  question.§  We  have 
already  given  a  brief  sketch  of  the  general  distribution  of  life  on 
the  globe  and  the  main  laws  on  which  it  depends.  We  have  seen 
that,  frequently,  one  part  of  the  fauna  of  a  land  region  appears  to  be 
indigenous,  but  another  part  to  be  made  up  of  colonists — the  latter 
of  course,  as  a  rule,  being  a  portion  of  the  fauna  indigenous  in 
another  region.  Suppose  that  among  these  immigrants  certain 
creatures  are  found  to  which  seas  would  be  an  insuperable  barrier, 
which  can  neither  fly  nor  swim,  such  as  most  mammals  and  certain 


*  See  pp.  365,  385. 

f  Such  as  are  now  found  at  depths  approaching  or  above  2000  fathoms.     See  p.  185. 

\  I  am  well  aware  that  during  the  last  few  years  several  such  deposits  have  been 
claimed  as  abyssal  muds  ;  but  when  these  are  found  associated  with  or  in  close  con- 
tiguity to  fairly  sandy  beds,  I  think  we  may  venture  to  question  the  accuracy  of  the  diag- 
nosis. Though  .every  abyssal  deposit  may  be  a  very  fine  mud,  the  converse  statement 
need  not  be  true. 

§  This  has  been  thoroughly  discussed  by  Dr.  A.  R.  Wallace  in  his  two  most  important 
works,  "  Island  Life"  and  "  The  Geographical  Distribution  of  Animals,"  and  a  critical 
summary  of  his  views  will  be  found  in  Dr.  W.  T.  Blanford's  Presidential  Address  to  the 
Geological  Society. — Quarterly  Journal,  xlvi.  (1890),  Proceedings,  pp.  59-107. 


488  THE    STORY  OF  OUR  PLANET. 

reptiles.  Their  presence  indicates  that  the  two  countries  must 
have  been  formerly  connected,  directly  or  indirectly.  If  the  num- 
ber of  the  common  forms  is  large  and  the  correspondence  close,  the 
severance  probably  is  comparatively  recent ;  if  the  contrary,  it  may 
go  back  to  very  remote  ages. 

It  has  been  found  that  the  faunas*  of  certain  regions,  at  present 
separated  by  wide  and  deep  seas,  contain  closely  allied  forms.  For 
example,  the  island  of  Madagascar  is  separated  from  Africa  by  a 
channel  about  250  miles  in  width  and  not  less  than  1 100  fathoms 
in  depth.  But  the  mammalia  of  Madagascar  are  related  to  those 
of  Africa  closely  enough  to  show  that  both  must  have  had  a 
common  origin,  or  the  countries  have  been  once  united.  The 
separation,  however,  probably  goes  far  back  into  Tertiary  times, 
for  only  two  genera  are  common  to  both  sides  of  the  Mozambique 
Channel.  One  of  these  is  a  species  of  river  hog  (Potamochcerus). 
This,  indeed,  can  swim,  but  in  all  probability  would  be  unable  to 
cross  a  strait  twenty  miles  in  width.  It  is,  then,  likely  that  at  a 
comparatively  late  epoch  in  the  Tertiary  era  Madagascar  was  not 
more  widely  separated  from  the  mainland  than  England  is  from 
France  at  the  present  time.  Similar  evidence  is  afforded  by  the 
birds,  reptiles,  batrachians,  and  fresh-water  fishes.  All  testify  not 
only  to  a  former  connection,  but  also  to  an  actual  severance  before 
the  numerous  genera,  which  at  present  are  especially  characteristic 
of  the  African  fauna,  migrated  thither  from  more  northern 
regions.f  But  the  fauna  of  Madagascar,  as  well  as  those  found  in 
the  Seychelles  and  the  Mascarene  Islands,  which  are  allied  to  the 
former,  suggest  also  that  a  connection  once  existed  between  this 
and  an  Oriental  region.  The  resemblances  are  more  marked 
among  fossils  than  among  recent  forms,  so  the  severance  probably 
took  place  at  a  very  ancient  date.  They  are,  however,  sufficient  to 
make  it  probable  that  so  late  as  the  Secondary  Era  there  was  a 
"land  union  between  India  and  South  Africa  across  the  Indian 
Ocean."  Mr.  Blanford,  after  a  careful  and  critical  review  of  the 
evidence  bearing  on  this  question,  comes  to  the  following  con- 
clusion :  "So  far  as  I  am  able  to  judge,  every  circumstance  as  to 
the  distribution  of  life  is  consistent  with  the  view  that  the  connec- 
tion between  India  and  South  Africa  included  the  Archaean  masses 
of  the  Seychelles  and  Madagascar,  that  it  continued  throughout 

*  The  same  is  true  of  the  flora  ;  but  we  restrict  ourselves  to  the  faunas  because,  on  the 
whole,  plants  are  more  readily  dispersed  than  animals. 

f  They  were  probably  driven  southward  by  the  cold  of  the  Glacial  epoch. 


PERMANENCE  OF  OCEAN  BASJNS  AND  LAND  AREAS.     4^9 

Upper  Cretaceous  times,  and  was  broken  up  into  islands  at  an  early 
Tertiary  date.  Great  depression  must  have  taken  place,  and  the 
last  remnants  of  the  islands  are  now  doubtless  marked  by  the  coral 
atolls  of  the  Laccadives,  Maldives,  and  Chagos,  and  by  the  Saya 
de  Malha  bank."* 

Again,  there  is  evidence  to  indicate  that  Australia  was  originally 
connected  with  New  Zealand  on  the  one  hand,  and  even  with 
South  America  on  the  other.  Yet  between  it  and  the  former  the 
channel  is  always  more  than  1000  fathoms  deep,  though  it  is  greatly 
narrowed  in  the  direction  of  Queensland  by  a  long  spur,  which 
extends  from  New  Zealand  toward  the  northwest,  while  Australia 
is  separated  from  the  American  continent  by  the  whole  breadth  of 
the  Pacific.  There  is,  however,  a  very  considerable  area  bordering 
the  Antarctic  land  region  over  which  the  sea  is  comparatively 
shallow,  but  this  plateau  is  separated  from  both  the  Australasian 
and  the  South  American  continents  by  a  fairly  broad  and  deep 
channel;  still  a  rise  of  about  1000  fathoms  would  increase  the  Ant- 
arctic area  to  continental  magnitude,  and  almost  link  it  with  the 
other  two,  when  they  were  correspondingly  enlarged. 

We  have  dwelt,  of  course,  upon  one  side  of  the  evidence,  and 
there  is  more  of  a  like  kind.  That  which  points  in  the  opposite 
direction  can  be  inferred  from  what  has  been  already  said  as  to  the 
distribution  of  life;  but  a  discussion  of  its  details  would  occupy 
more  space  than  can  be  spared.  On  the  whole,  however,  Dr.  Blan- 
ford's  conclusion  seems  fully  warranted  by  the  facts — namely,  that 
"while  the  general  permanence  of  ocean  basins  and  continental  areas 
cannot  be  said  to  be  established  on  anything  like  firm  proof,  the 
general  evidence  in  favor  of  this  view  is  very  strong.  But  there  is 
no  evidence  whatever  in  favor  of  the  extreme  view  accepted  by 
some  physicists  and  geologists  that  every  ocean  bed,  now  more 
than  1000  fathoms  deep,  has  always  been  ocean,  and  that  no  part 
of  the  continental  area  has  ever  been  beneath  the  deep  sea.  Not 
only  is  there  clear  proof  that  some  land  areas  lying  within  conti- 
nental limits  have  at  a  comparatively  recent  date  been  submerged 
over  1000  fathoms,  while  sea  bottoms  now  over  1000  fathoms  deep 
must  have  been  land  in  part  of  the  Tertiary  era,  but  there  are  a 
mass  of  facts,  both  geological  and  biological,  in  favor  of  land  con- 
nection having  formerly  existed  in  certain  cases  across  what  are 


*  Presidental  Address,  Quarterly  Journal  of  the  Geological  Society,  xlvi.  (1890),  p.  98 
(Proceedings). 


496  THE  STORY  OP  OUR  PLACET. 

now  broad  and  deep  oceans."  In  other  words,  we  might  venture  to 
say:  Continents  may  be  broken  up  into  groups  of  islands,  and  may 
be  again  united ;  they  may  be  augmented  by  the  conversion  into 
mountain  zones  of  considerable  tracts,  which  once  formed  marginal 
areas  of  submarine  deposit,  and  the  peculiar  tendency  to  "dimple"* 
which  is  exhibited  by  the  earth's  crust  may  lead  to  the  formation 
locally  of  deep  basins  among  the  island  groups.  In  like  way  the 
bed  of  an  ocean  may  locally  buckle  up,  or  a  tract  of  land  may  be 
involved  in  an  extensive  downbending  of  the  earth's  crust.  Never- 
theless it  is  more  probable,  on  the  whole,  that  continents  indicate 
regions  over  which  land  has  dominated  from  very  early  days,  and 
that  the  profounder  depths  of  the  ocean  basins  mark  the  centers  of 
large  areas  which  have  been  even  more  persistently  submerged. 

*  See,  among  others,  the  curious  basins  in  the  Banda  and  Celebes  Seas,  that  between 
New  Guinea  and  the  Caroline  Islands,  and  the  deep  hole  found  by  the  Challenger  south  of 
the  Ladrone  Islands. 


CHAPTER  III. 

CLIMATAL   CHANGE:   ITS   CAUSE   AND   HISTORY. 

AT  a  geological  epoch  comparatively  recent  the  climate  of  this 
country,  probably  also  of  a  large  part  of  the  northern  hemisphere, 
was  much  colder  than  it  is  at  present ;  at  one,  much  more  remote, 
it  was  almost  certainly  considerably  warmer.*  Is  it  possible  to 
account  for  these  changes?  The  climate  of  any  place  depends 
primarily  upon  its  latitude,  secondarily  upon  its  position  in  regard 
to  the  sea,  and  a  number  of  other  less  direct  causes,  such  as  the 
influence  of  winds  and  ocean  currents,  the  distribution  of  land  and 
water  (i,  e.,  whether  its  position  is  continental  or  insular),  and  the 
like.  The  climate,  in  short,  of  any  locality  is  the  result  of  many 
complicated  conditions,  and  the  courses  of  the  isothermal  lines  at 
the  present  day  by  no  means  correspond  with  the  circles  of  lati- 
tude. This  is  true  of  both  the  monthly  and  the  annual  isotherms. 
For  instance,  the  summer  isotherm  of  59°  F.  passes  through  the 
north  island  of  Japan  to  near  Kolymsk,  and  takes  a  fairly  regular 
course  through  Asia  to  Archangel,  whence  it  goes  by  the  top  of 
the  Gulf  of  Bothnia  to  Edinburgh  and  Belfast;  from  Ireland  it 
crosses  the  Atlantic  to  America,  running  north  of  Quebec,  and  across 
the  continent  to  north  of  Vancouver  Island.  Between  its  highest 
latitude  on  the  continents  of  Asia  and  America  and  its  lowest  on 
the  ocean  there  is  found  a  difference  of  more  than  twenty  degrees. 
If  we  follow  the  winter  isotherm  of  5°  F.  (which  also  passes  through 
Archangel)  we  find  that  it  runs  to  that  city  from  St.  Lawrence 
Island  (south  of  Behring  Strait)  through  Central  Siberia  and  Oren- 
berg;  it  then  grazes  the  top  of  the  Gulf  of  Bothnia,  rising  thence 
sharply  northward  to  the  south  of  Spitzbergen,  whence  it  slopes 
down  to  pass  to  the  south  of  Disco  Bay,  in  Greenland,  and  then  by 
Lake  Superior  across  the  American  continent.!  The  difference  of 
latitude  between  the  extreme  positions  on  its  course  amounts  to 
over  twenty-five  degrees.  Lastly,  the  path  of  the  annual  isotherm 
of  32°,  to  which  we  shall  have  to  refer  again,  exhibits  an  irregularity 

*  See  pp.  393-396  and  470,  471. 

f  Its  course  is  roughly  parallel  to  that  of  the  line  of  32°  in  the  annexed  chart. 

491 


49* 


THE   STORY  OF  OUR  PLACET. 


no  less  marked.  It  "descends  in  Eastern  Siberia  rather  south  of  the 
latitude  of  London ;  it  rises  very  gradually  as  it  proceeds  westward 
as  far  as  Tobolsk  (lat.  58°  21'),  whence  it  ascends  more  rapidly  to 
Archangel,  and  then  twists  up  in  an  S-like  curve  through  the  north 
end  of  the  Gulf  of  Bothnia,  overleaps  the  North  Cape,  and  passes 
within  the  7Oth  parallel  of  latitude;  thence  it  gradually  falls, 
grazes  the  northwest  coast  of  Iceland,  cuts  Greenland  a  little  to  the 


FIG.  164.— MEAN  ANNUAL  ISOTHERMS  OF  THE  NORWEGIAN  SEA. 

(The  numbers  denote  degrees  Centigrade.) 

north  of  Cape  Farewell,  and  descends  to  Labrador.  Here  its  path 
for  a  time  is  more  even,  for  it  runs  almost  along  the  5oth  parallel 
through  the  south  end  of  Hudson  Bay,  after  which  it  rises  gradu- 
ally until  it  passes  along  the  promontory  of  Alaska."*  There  are, 
accordingly,  considerable  tracts,  both  in  Eastern  Asia  and  in 
Northern  America,  in  which  the  mean  annual  temperature  is  less 
than  32°.  In  the  southern  hemisphere  also  the  temperature  is 
lower  than  that  of  England  in  corresponding  latitudes.  "The  mean 
temperature  of  Tierra  del  Fuego  is  42°  F.  These  islands  corre- 
spond roughly  in  latitude  with  the  eastern  counties  of  England, 

*  This  and  the  following  extracts  are  from  an  article  by  the  author,  on  "  Geographical 
Changes  and  the  Glacial  Epoch,"  in  the  Contemporary  Review,  1891,  p.  716. 


CLIMATAL   CHANGE :  ITS  CAUSE  AND  HISTORY. 


493 


where  the  temperature  is  seven  or  eight  degrees  higher.  That  of 
South  Georgia,  which  corresponds  in  position  with  the  latitude  of 
York,  exhibits  a  similar  difference.  Here  the  climate  is  most 
inclement,  the  mercury,  even  during  a  midsummer  day,  not  rising 
more  than  ten  degrees  above  the  freezing  point."  In  the  Straits  of 
Magellan  the  temperature  is  quite  eight  degrees  below  that  of  cor- 
responding positions  in  North  Wales.  In  short,  the  climate  of 


FIG.  165. — DIAGRAM  OK  THE  COURSE  OF  THE  WINTER  ISOTHERMS  IN  THE 
NORTHERN  HEMISPHERE. 

Great  Britain,  much  as  it  is  abused,  is  abnormally  warm,  owing  to 
influences  which  have  been  already  mentioned.*  It  is  not,  how- 
ever, sufficient  to  suppose  them  removed,  for  any  explanation  of 
the  low  temperature  of  the  Glacial  epoch  must  apply  to  Europe,  at 
any  rate  from  Scandinavia  to  the  Alps,  and  to  North  America. 

By  what  amount  must  the  temperature  have  been  lowered?  The 
answer  to  this  question  depends  to  some  extent  upon  the  limits 
assigned  to  the  land  ice,  on  which  point  opinions  differ,  but  if  we 
take  the  more  restricted  limits—  i.  e.,  those  accepted  by  the  most 
moderate  school  of  glacialists,  we  shall  have  ascertained  what  is  the 
least  possible  change.  Glaciers  will  not  form  till  the  temperature 
is  rather  below  32°  F.  If  Wales  is  to  produce  large  ice-streams 

*  In  Part  I.,  ch.  iii.  and  iv. 


494 


THE   STORY  OF  OUR  PLANET. 


the  temperature  at  the  seacoast,  which  is  now  50°  F.,  must  be 
lowered  by  about  18°  F.  Perhaps  even  this  would  barely  suffice ;  so 
we  may  say  that  all  geologists  would  agree  that,  in  part  of  the  great 
Ice  Age,  the  temperature  of  the  British  Isles  must  have  been  lower 
than  at  present  by  not  less  than  20°  F.  The  huge  ice-sheets  which 
once  flowed  from  the  Alps  might  be  brought  back  by  a  drop  of 
1 8°  F. ;  that  of  North  America,  which  was  yet  more  gigantic,f 


FIG.  166.— DIAGRAM  OF  THE  COURSK  OF  THE  ANNUAL  ISOTHERMS  IN  THE 
NORTHERN  HEMISPHERE. 

might  be  restored,  if  other  conditions  were  favorable,  by  a  lowering 
amounting  to  about  16°  F. 

By  what  changes  could  this  alteration  of  temperature  be  made? 
So  far  as  Britain  is  concerned,  a  general  rise  of  the  land  would  have 
a  double  effect.  It  would  increase  not  only  the  height  of  the 
mountains,  but  also  their  distance  from  the  sea.  Suppose  North 
Wales  to  receive  a  further  elevation  of  2000  feet ;  this  alone  would 
make  a  difference  of  7°  F.,*  to  which,  perhaps,  in  the  case  of  the 
Carnarvonshire  lowlands,  4°  F.  should  be  added  for  increased  dis- 
tance from  the  sea.  This  would  account  for  fully  half  the  amount 
required.  But  it  is  generally  estimated  that  at  the  present  time 


*Seep.  425. 

f  As  a  rough  average  we  may  take  i°  F.  for  each  300  feet  of  ascent. 


CLIMATAL    CHANGE:  ITS    CAUSE  AND  HISTORY.  495 

the  climate  of  this  part  of  Wales  is  raised  by  the  effects  of  the  Gulf 
Stream — in  the  opinion  of  some  authorities,  as  much  as  7.5°  F.  If, 
in  addition,  that  current  were  diverted,  the  temperature  might  be 
lowered  by  about  18°  F. — that  is  to  say,  the  cold  would  probably 
be  as  great  as  it  was  in  all  but  the  severest  part  of  the  Glacial 
epoch.  A  like  elevation  would  produce  a  similar  effect  in  both  the 
Alps  and  Canada,  but  here  the  Gulf  Stream  must  not  be  taken  into 
consideration,  since  on  the  former  it  has  little  influence,  and  in  the 
latter  none  at  all.  So  in  all  these  cases  such  an  amount  of 
geographical  change  as  might  be  called  reasonable  would  fail,  even 
under  the  most  favorable  circumstances,  to  give  a  temperature  suffi- 
ciently low.* 

The  southern  hemisphere  emphasizes  the  fact  that  a  somewhat 
abnormally  mild  climate  is  enjoyed  by  the  western  side  of  Europe, 
especially  in  winter  time,  but  it  does  not  provide  an  instance  of  a 
temperature  at  any  corresponding  latitude  low  enough  to  be  com- 
pared with  that  of  Britain  in  the  Glacial  epoch.  We  might,  how- 
ever, be  asked:  Is  this  material  to  the  inquiry?  for  have  we  not 
already  admitted  that  there  are  places  in  the  northern  hemisphere 
itself  with  a  temperature  20°  lower  than  that  of  the  British  Islands? 
This  is  true,  but  we  must  not  forget  that  to  place  the  latter  under 
similar  circumstances  to  the  former  would  require  physical  changes 
on  a  scale  far  greater  than  would  be  justifiable  at  this  late  geolog- 
ical age.  Some  geologists  hesitate  to  concede  the  possibility  of  a 
movement,  either  in  an  upward  or  in  a  downward  direction,  of  as 
much  as  1500  feet.f  We  certainly  cannot  venture  to  convert  the 
Atlantic  into  a  continent ;  and  if  this  were  done  without  some 
extensive  compensation,  it  is  doubtful  whether,  however  severe  the 
cold  might  be,  the  air  would  not  be  too  dry  for  the  production  of 
an  ice-sheet.  In  fact,  each  attempt  to  account  for  the  Glacial 
epoch  solely  by  terrestrial  causes  places  us  on  the  horns  of  some 
dilemma. 

*  Of  course,  if  we  are  right  in  supposing  that  a  good  deal  of  the  English  bowlder  clay 
was  formed  under  water,  elevation  could  not  be  assumed  at  a  time  when  a  seashore  temper- 
ature of  32°  F.  (annual)  with  a  severe  winter  climate,  would  be  required.  There  is,  how- 
ever, evidence  (page  395)  that  just  before  the  Glacial  epoch,  perhaps  also  at  the  time  of 
the  largest  ice-sheets,  the  land  stood  higher  than  at  present.  Possibly  in  this  country  the 
time  of  maximum  cold  did  not  correspond  with  that  of  maximum  elevation. 

f  The  peculiar  powers  of  ice-sheets  in  collecting  specimens  from  the  sea-bottom  and 
transporting  them  to  inland  localities,  referred  to  on  page  396,  have  been  devised  to  escape 
from  this  supposed  difficulty  of  a  downward  movement  of  the  above  amount  during  Glacial 
jepoch, 


496 


THE   STORY  OF  OUR  PLANET. 


But  even  if  all  these  difficulties  were  successfully  overcome,  if 
land  and  water  were  so  arranged  as  to  bring  about  the  low  tempera- 
ture required,  we  are  then  called  upon  to  account  for  an  elevation 
of  temperature  not  less  marked.  It  has  been  estimated  that  the 
climate  of  Switzerland  in  Miocene  times  was  about  16°  F.  above 
what  it  is  at  present,  and  in  the  preceding  period  higher  still  by 
perhaps  4°  F.  The  fauna  and  flora  of  the  Eocene  in  England  con- 
cur in  indicating  a  temperature  which  was  at  the  least  20°  F.  above 


JIG.  167. — SURFACE  ISOTHERMS  OF  THE  SEA  IN  JANUARY  AND  FEBRUARY, 
INDICATIVE  OF  PROBABLE  EFFECTS  OF  GULF  STREAM. 

(The  numbers  denote  degrees  Centigrade.) 


that  of  London ;  yet  we  have  already  observed  that  the  English 
climate  is  now  abnormally  warm. 

Prior  to  the  Tertiary  era  the  fauna  and  flora*  differ  so  much  from 
that  which  now  exists  that  it  is  extremely  difficult  to  use  them  in 
making  inferences  as  to  the  climatal  conditions  which  may  have 
existed  in  any  part  of  the  earth.  The  evidence,  however,  such  as 

*  Strictly  speaking,  the  flora  approaches  the  present  type  a  little  earlier,  i.  e. ,  at  the  end 
of  the  Neocomian  period, 


CLIMATAL    CHANGE:    ITS  CAUSE  AND  HISTORY.  497 

it  is,  suggests,  on  the  whole,  a  climate  warmer  rather  than  colder 
than  it  is  at  present.  At  any  rate,  there  is  little  indication  of  any- 
thing like  a  Glacial  epoch.  Bowlders  here  and  there,  as  in  the 
chalk,  or  even  in  the  coal,  may  suggest  the  possibility  of  floating 
ice ;  but  in  this,  supposing  rather  different  geographical  conditions, 
there  would  be  nothing  surprising.  The  curious  breccias  and  large 
bowlders*  in  the  flysch  of  the  Alps,  and  those  described  by  Pro- 
fessor Juddf  in  the  Upper  Oolite  of  Sutherlandshire,  suggest  the 
action  of  ice.  The  Permian  breccias  of  Central  England;}:  and  the 
bowlders  in  the  Talchir  group  of  India  §  (to  mention  no  other 
cases)  suggest  the  possibility  that  a  low  temperature  was  generally 
prevalent  somewhere  about  the  epoch  when  the  Primary  passed 
into  the  Secondary  era.  Still  the  evidence  of  anything  comparable 
with  the  conditions  during  the  Glacial  epoch  is  extremely  doubtful, 
if,  indeed,  it  be  not  wholly  wanting. 

Sir  J.  Evans  has  suggested  an  hypothesis  which  would  afford  a 
ready  explanation  of  climatal  change.  Supposing  the  earth  to  con- 
sist of  a  solid  outer  shell  resting  on  a  fluid  interior,  the  transference 
of  sediment  from  place  to  place,  and  the  upheaval  of  mountain 
chains,  may  make  a  change  in  the  direction  of  the  axis  of  rotation 
of  this  shell,  while  that  of  the  mass,  as  a  whole,  is  practically  unaf- 
fected. The  shell  accordingly  will  slip  over  the  inner  mass  into  a 
new  position,  and  the  geographical  station  of  the  poles  will  be 
altered.  It  may  be  doubted,  however,  whether  the  fluidity  of  the 
interior  would  be  such  as  to  permit  of  any  sliding  about  of  the 
crust  except  under  conditions  so  extreme  as  to  be  very  improbable, 
and  mathematicians  assert,  after  making  calculations,  that  no 
change,  which  may  be  regarded  as  practically  possible,  would  affect 
the  position  of  the  poles  by  more  than  two  or  three  degrees.  The 
hypothesis  also  would  not  be  any  real  help  in  explaining  the 
climate  of  the  Glacial  epoch,  for  palaeontological  evidence  shows 

*  In  the  Habkerenthal,  near  Interlaken,  these  are  sometimes  about  thirty  cubic  yards  in 
volume  ;  near  Sepey,  Val  des  Ormonds,  they  are  almost  as  large.  It  should  be  stated 
that  opinions  differ  as  to  the  mode  of  transport  of  these  bowlders,  and  to  attribute  it  to  ice 
raises  some  serious  difficulties,  because,  as  has  been  just  said,  a  warm  climate  seems  to 
have  prevailed  in  the  earlier  part  of  the  Eocene,  and  the  Alps  were  not  upraised  till  a  later 
epoch,  so  that  the  glaciers  of  a  mountain  chain  seem  to  be  excluded. 

\  Quarterly  Journal  of  the  Geological  Society,  1873,  P-  I§7- 

\  See  a  Paper  by  the  author  in  the  Midland  Naturalist,  1892,  February  and  March. 

§  Bowlders  (striated)  also  occur  in  the  Olive  group  (Geological  Magazine,  1886,  pp.  492, 
494)  ;  to  this,  however,  some  geologists  assign  a  date  which  would  bring  it  not  far  away 
from  that  of  the  flysch. 


49 8  THE    STORY  OF  OUR  PLANET. 

that  in  Tertiary,  perhaps  even  in  later  Secondary  times,  climatal 
zones  existed  on  the  earth  in  positions  generally  similar  to  those 
which  they  at  present  occupy. 

Is  it,  then,  possible  to  find  an  explanation  by  looking  beyond  the 
surface  of  the  earth?  Some  geologists  have  suggested  that  the 
solar  system  in  its  course  through  space  may  traverse  regions  espe- 
cially cold  or  warm.  This,  however,  is  really  taking  a  leap  in  the 
dark  to  avoid  a  difficulty,  for  there  is  little,  if  any,  evidence  in  sup- 
port of  the  hypothesis.  Others  have  suggested  that  the  sun  may 
be  a  variable  star.  This  is  not  in  itself  impossible,  but  in  such  case 
either  the  elevation  of  temperature  would  be  rapid,  though  followed 
by  a  slow  cooling,  or,  if  the  changes  are  both  gradual,  we  cannot 
say  how  they  are  to  be  explained,  and  cannot  find  any  proof  of 
their  occurrence.  Moreover,  if  the  fire  needs  to  be  occasionally 
stirred,  to  speak  figuratively,  it  is  difficult  to  understand  how  the 
poker  is  to  be  applied  without  a  considerable  risk  to  the  complete 
stability  of  the  solar  system.  Astronomy,  however,  discloses  certain 
departures  from  a  periodic  uniformity  which  can  hardly  fail  to  pro- 
duce some  effect  on  the  climate  of  the  globe  or  of  particular  regions. 

In  the  first  place,  the  form  of  the  orbit  described  by  the  earth 
about  the  sun  is  not  fixed,  but  is  constantly  varying  within  certain 
limits,  though  with  extreme  slowness — it  may  be  almost  a  circle,  or 
it  may  be  more  elliptical  than  at  present.  Although  this  change  of 
form  does  not  much  alter  the  total  amount  of  heat  received  in  a 
year,  it  very  materially  affects  the  distribution,  because  the  more 
elliptical  the  orbit,  the  more  unequal  in  length  are  the  seasons. 
Thus  the  one  hemisphere  will  have  a  long  summer  and  a  short 
winter,  while  the  other  has  a  short  summer  and  a  long  winter. 
Moreover,  in  the  latter  case  the  summer  will  occur  when  the  earth 
is  at  its  perihelion  distance,  and  the  winter  when  it  is  in  aphelion — 
so  that  the  one  season  will  be  comparatively  short  and  hot, 
the  other  long  and  cold — while  in  the  other  hemisphere  the  sum- 
mers will  be  longer,  but  cooler,  and  the  winters  shorter  and  milder. 

Even  very  competent  judges  are  by  no  means  agreed  as  to  the 
effects  which  would  be  produced  on  climate  by  any  possible  changes 
in  the  form  of  the  earth's  orbit.  All  admit  that  the  total  amount 
of  heat  received  during  a  year  would  be  only  slightly  altered,  but 
some  maintain,  with  Sir  R.  S.  Ball,  that  the  changed  distribution 
of  it  would  produce  a  material  effect.  This  is  an  outline  of  his 
development  of  an  argument  already  advanced  by  the  late  Dr.  Croll 
and  others.  There  can  be  no  question  that  the  heat  of  the  sun  is 


CLIMATAL    CHANGE:    ITS  CAUSE  AND   HISTORY. 


499 


the  sole  factor  of  any  importance  in  raising  the  surface  of  the  earth 
to  its  present  temperature.  But  for  that  this  surface  would  be 
speedily  chilled  down  to  the  temperature  of  space.  Assuming  the 
quantity  of  heat  emitted  by  the  sun  to  be  constant,  the  amount 
which  any  place  receives  at  a  particular  moment  depends  upon  its 
position  on  the  globe  and  that  of  the  earth  in  its  orbit.  Changes  in 
the  form  of  the  orbit,  as  already  said,  do  not  materially  affect  the 


FIG.  168.— DIAGRAM  OF  AN  ELLIPTICAL  ORBIT. 

A,  A',  Major  Axis  ;  »,  B',  Minor  Axis  ;  c,  Center  ;  s,  H,  Foci  (s,  marking  position  of  sun).  Suppose  L  L'  to 
indicate  the  position  of  the  equinoxes,  then  it  will  be  seen  from  the  diagram  that  the  seasons  are. 
very  unequal  in  length.  It  must  be  remembered  that  the  line  L  S  i.'  changes  in  position,  as  indicated 
by  /s  /'. 


total  quantity  of  heat  received  by  the  earth  as  a  whole ;  also  equal 
amounts  are  received  in  the  perihelion  and  the  aphelion  portions  of 
the  orbit,  as  they  may  be  called.  This,  however,  is  only  true  of 
the  earth  as  a  whole ;  the  amount  of  heat  received  by  a  particular 
hemisphere  in  its  summer  and  its  winter  season  is  always  in  the  pro- 
portion of  the  numbers  63  and  37.  The  seasons,  as  already  said, 
vary  in  length,  but  the  greatest  possible  difference  between  them 
amounts  to  33  days — i.  e.,  the  one  may  be  166,  the  other  199  days. 
Suppose,  then,  that  in  England  (and  in  the  northern  hemisphere 
generally)  the  winter  season  is  199  days  long,  and  that  during  this 
period  only  37  per  cent,  of  the  total  supply  of  heat  is  received,  this 
would  produce  a  low  temperature.  For  the  summer  there  is  a 
larger  share  distributed  over  a  shorter  time.  Sir  R.  S.  Ball  illus- 


500  THE   STORY  OF  OUR  PLANE7\ 

trates  the  conditions  which  would  prevail  in  the  two  hemispheres 
by  the  following  calculations: 

EXTREME  CONDITIONS. 

Northern  hemisphere        \  Mean  daily  heat  |n  summer  <short)       •  '     T'38 
(  Mean  daily  heat  in   winter   (long)         .  .        .68 

Southern  hemisphere         \  Mean  daily  heat  in  summer  (lonS>          '     ''l6 
(Mean   daily  heat  in  winter  (short)         ..       .81 

PRESENT  CONDITIONS. 

Northern  hemisphere        \  Mean  dai^  heat  in  summer  <l86  **&     •  •     *'2* 
(  Mean  daily  heat  in  winter  (179  days)       .  .     0.75 

He  makes  use  of  a  rough  and  homely  comparison  to  illustrate  the 
different  conditions  of  a  hemisphere  under  these  altered  circum- 
stances. Suppose  a  man  to  have  a  fixed  salary,  which  is  paid  in 
unequal  installments.  Let  this,  for  example,  be  £100  a  year,  and 
let  it  be  divided  into  portions  of  £63  and  ^37,  which  must  be 
expended  in  the  seasons  for  which  they  are  paid.  When  there  is 
the  longest  possible  summer  and  the  shortest  possible  winter,  the 
man's  daily  portion  amounts  for  the  one  to  6s.  4^.,  for  the  other  to 
4-y.  $l/2d>—  "under  these  circumstances,  he  enjoys  a  fairly  beneficent 
arrangement."  Now  suppose  the  circumstances  reversed :  his  sum- 
mer daily  allowance  is  js.  jd.,  but  this  comparative  luxury  has  to  be 
expiated  in  the  winter,  for  then  his  allowance  is  only  ~$s.  $>y2d*  The 
illustration  obviously,  as  its  author  would  admit,  does  not  repre- 
sent the  real  circumstances  of  the  case,  but  it  helps  in  giving  some 
idea  of  the  marked  contrast  in  the  temperatures  of  the  midsummer 
and  midwinter  months,  which  might  result  from  an  extreme  eccen- 
tricity. 

Indirect  causes,  however,  would  probably  affect  the  climate  under 
these  exceptional  conditions,  and  tend  to  increase  the  inclemency. 
By  the  end  of  the  winter  snow  and  ice  would  have  accumulated  in 
considerable  quantities,  and  no  very  material  rise  in  temperature 
could  be  produced  until  these  were  melted.  During  the  thaw  the 
air  would  be  saturated  with  vapor,  and  clouds  would  be  constantly 
forming.  Thus,  as  soon  as  the  sun  began  to  produce  an  improve- 
ment, it  would,  like  an  injudicious  reformer,  arouse  an  opposition, 
which,  to  a  certain  extent,  would  counteract  its  benefits;  so  that, 
although  the  amount  of  heat  transmitted  ought  to  have  made  the 
summers  warm,  they  actually,  in  all  probability,  would  be  rather 

*  Sir  R.  S.  Ball,  "  The  Cause  of  an  Ice  Age,"  p.  122. 


CLIMATAL    CHANGE:  ITS  CAUSE  AND  HISTORY.  501 

cold.  Even  if  it  may  be  assumed  that  a  change  in  the  form  of  the 
earth's  orbit  produces  a  corresponding  change  in  the  climate  of  each 
hemisphere,  we  have  not  yet  exhausted  the  possible  causes  of  altera- 
tion. The  actual  position  of  the  orbit  varies,  and  the  axis  about 
which  the  earth  rotates  does  not  remain  always  parallel  to  itself. 
These  movements  are  complicated  in  character.  The  principal 
one — that  of  precession — has  been  already  explained,*  but  there 
are  others  as  well.  Let  us  recur  to  our  original  illustration,  the 
knitting  needle  inserted  into  the  model  of  the  sun ;  this,  in  conse- 
quence of  the  movement  just  named,  slowly  and  majestically 
sweeps  out  a  cone  in  space,  completing  the  figure  in  25,868  years. 
But  if  we  look  more  closely,  we  shall  see  that  the  cone  is  not  per- 
fectly uniform.  The  needle  sways  slightly  backward  and  forward. 
Its  motion  is  twofold ;  one,  if  no  other  effect  had  to  be  observed, 
would  cause  it  to  describe  a  very  tiny  ellipse,f  and  this,  when  com- 
bined with  the  precessional  movement,  would  produce  a  slight 
"frilling"  of  the  surface  of  the  cone.  The  other  motion  is  rather 
more  important,  but  is  less  regular — less  periodic,  to  use  a  more 
technical  term.  It  is  due  to  an  oscillation  of  the  earth's  axis  back- 
ward and  forward  for  a  space  of  about  i°  22'  on  either  side  of 
23°  28',  which  was  roughly  its  deviation  from  a  vertical  position 
in  18014 

The  effect  of  this  movement  is  to  increase  or  diminish  the  trop- 
ical and  polar  regions,  and  correspondingly  to  restrict  or  enlarge  the 
temperate  zones.  For  example  :  if  it  be  winter  time  in  the  northern 
hemisphere  when  the  angle  has  its  greatest  value,  the  sun  would 
not  be  seen  at  the  December  solstice  anywhere  north  of  the  top  of 
the  Gulf  of  Bothnia,§  an(^»  further  south,  would  not  be  so  high  in 
the  midday  sky  by  nearly  a  degree  and  a  half.  This  ought  to  pro- 
duce a  more  marked  difference  between  summer  and  winter,  and  to 
affect  broad  marginal  zones,  if  nothing  more,  in  the  temperate 
regions-!  The  results,  however,  of  this  change  would  not  be  great, 
while  we  may  venture  to  pronounce  those  of  the  former  one  quite 
inappreciable. 

But  the  effect  of  the  precessional  movement  ought  to  be  impor- 

*P.  315. 

f  The  diameter   is  only  18.5  seconds. 

|  Strictly  speaking,  this  is  due  to  an  oscillation  of  the  plane  of  the  orbit,  as  if,  when  a 
top  was  spinning  on  a  table,  that  were  very  slightly  tilted  up  and  down. 
§  More  strictly  speaking,  lat.  65°  10'  N. 
|  The  effect  of  this  change  is  discussed  by  Dr.  Croll  in  "  Climate  and  Time,"  ch.  xxv. 


5°2  THE   STORY  OF  OUR  PLANET. 

tant.  This,  however,  must  be  regarded  in  combination  with 
another  movement  already  mentioned.  Suppose  the  orbit  repre- 
sented by  an  oval  groove  cut  in  the  surface  of  a  table,  and  the  earth 
by  a  top,  and  that  as  the  latter  is  spinning  in  the  grove  the  table 
itself  is  slowly  turning  round.  The  combination  of  this  second 
movement  with  that  of  precession  brings  about  a  repetition  of  past 
conditions  more  quickly  than  would  be  effected  by  the  latter  alone; 
so  that  the  earth's  axis  of  rotation  becomes  parallel  to  its  original 
position,  not  in  25,868  years,  as  mentioned  above,  but  in  21,000 
years.  The  effect  of  the  precessional  movement,  if  the  northern 
hemisphere  be  taken  as  an  example,  is  as  follows:  In  the  year  1248 
A.  D.  midwinter  occurred  when  the  earth  was  in  perihelion,  or  at  its 
nearest  distance  from  the  sun,  and  so  midsummer  corresponded 
with  the  aphelion  position.  But  about  the  year  9250  B.  c.  the  sea- 
sons fell  under  circumstances  exactly  the  opposite,  and  these  will 
recur  about  11,750  A.  D.  Whatever  effects,  then,  precession  may 
produce,  they  ought  to  alternate  with  some  regularity  ;  for  the  form 
of  the  earth's  orbit  changes  very  slowly,  and  the  cycle  of  the  preces- 
sional movement  might  be  completed  once  or  twice  during  the  time 
when  the  eccentricity  was  near  its  maximum.  Accordingly,  the 
effects  of  the  latter  would  be  either  intensified  or  mitigated  in  a 
particular  hemisphere  by  the  action  of  the  former.  For  instance, 
about  9250  B.  c.  winter  in  the  northern  hemisphere  fell  in  aphelion 
and  summer  in  perihelion;  hence  if  at  that  time  the  eccentricity 
of  the  orbit  had  been  rather  high,  the  cold,  as  already  intimated, 
would  have  been  severe,  and  the  climate  generally  ungenial.  But 
the  conditions  in  the  southern  hemisphere  would  have  been 
reversed,  and  the  results  very  different.  So  far,  then,  as  precession 
goes,  the  northern  hemisphere  has,  for  a  time,  seen  its  best  days; 
but,  as  a  set-off  to  this,  the  eccentricity  is  now  diminishing. 

Some  geologists  believe  that  the  deposits  belonging  to  the  Glacial 
epoch  indicate  at  least  one  alternation  of  mild  with  severe  climates, 
and  attribute  this  to  the  effect  of  precession.  If  such  there  be,  the 
explanation  would  probably  be  adequate  for  the  purpose,  but  the 
value  of  the  evidence  on  which  these  so-called  "Interglacial  "  ages 
depend  is  by  no  means  universally  admitted.  Some  geologists  are 
of  opinion  that  the  oscillations  in  the  magnitude  of  the  glaciers 
were  not  greater  than  may  be  explained  by  changes  of  level  or  by 
climatal  variations  of  a  minor  character,  such  as  even  now  cause 
considerable  fluctuations  in  the  size  of  Alpine  glaciers.  These 
would  make  their  effects  still  more  perceptible  on  the  greater  ice- 


CLIMATAL   CHANGE  :  ITS  CAUSE  AND  HISTORY.  503 

streams,  just  as  a  water  barometer  is  more  conspicuously  sensitive 
than  a  mercurial. 

In  the  present  state  of  our  knowledge  we  are  not  in  a  position  to 
express  a  very  positive  opinion  as  to  the  causes  by  which  the 
climate  of  either  hemisphere  has  been  affected.  The  subject  is  an 
extremely  difficult  and  intricate  one,  and  the  most  competent  judges 
are  still  at  issue  as  to  whether  astronomical  changes  would  or  would 
not  produce  any  very  material  effects.  So  far  as  I  can  form  an  opin- 
ion it  seems  to  me  certain  on  the  one  hand  that  geographical 
changes  would  be  sufficient  to  produce  very  marked  alterations  in 
climate,  but  very  doubtful  on  the  other  whether  any  such  changes 
which  could  be  reasonably  assumed  at  so  late  a  time  would  be  suf- 
ficient to  account  for  the  existence  of  a  very  low  temperature  in  so 
large  a  portion  of  the  northern  hemisphere  during  the  colder  part  of 
the  Glacial  epoch.  It  seems  also  highly  probable  that  changes  in 
the  eccentricity  of  the  orbit  and  the  results  of  the  precessional  move- 
ment would  have,  in  general,  the  effects  which  have  been  ascribed 
to  them  above;  the  latter  now  intensifying,  now  tending  to  neutral- 
ize the  former.  So  I  regard  the  climate  of  any  region,  to  use  a 
mathematical  phrase,  as  a  function  of  three  independent  variables, 
which  may  at  one  time  co-operate,  at  another  time  counteract  one 
another.  In  the  one  case,  they  may  produce  either  a  Glacial  epoch 
or  an  exceptionally  warm  period ;  in  the  other,  the  climate  of  any 
region  may  remain  fairly  normal — that  is,  may  depend  mainly  upon 
latitude,  or,  at  any  rate,  be  little  affected  by  astronomical  causes. 
But  I  am  doubtful  whether  even  these  causes,  as  at  present  under- 
stood, supply  us  with  a  complete  explanation,  for  both  the  Glacial 
epoch  and  the  long-continued  warmth  of  the  Eocene  and  Oligocene 
periods,  so  far  as  we  know,  are  unique  of  their  kind.  I  am  accord- 
ingly disposed  to  think  that  either  something  remains  to  be  learned 
about  the  effects  of  one  or  more  of  these  variables,  or  some  other 
factor  affecting  climate  exists  which  is  as  yet  unappreciated. 

If,  however,  Dr.  Croll  be  right  in  considering  the  changes  of 
temperature,  of  which  we  have  spoken,  to  be  largely  due  to  varia- 
tions in  the  eccentricity  of  the  earth's  orbit,  it  should  be  possible  to 
determine  the  period  at  which  some  of  the  latest  of  these  occurred ; 
perhaps  even  to  construct  an  approximate  chronology  for  the  con- 
cluding chapters  of  the  earth's  history.  If  a  formula  could  be 
obtained  to  express  the  value  of  the  eccentricity  at  any  time, 
directly  or  indirectly,  in  terms  of  the  number  of  years  which  have 
separated  that  time  from  a  certain  date,  the  determination  of  this 


5 °4  THE   STORY  OF  OUR  PLANET. 

number  becomes  merely  a  question  of  arithmetic.  This  difficult 
problem  engaged  the  attention  of  an  eminent  mathematician  (the 
late  M.  Leverrier),  and  he  succeeded  in  constructing  a  formula 
which  is  believed  to  hold  good,  at  any  rate  approximately,  for  four 
millions  of  years,  past  and  future.  From  this  formula  the  late  Dr. 
Croll  calculated  the  eccentricity  of  the  earth's  orbit,  at  intervals  of 
50,000  years,  for  three  million  years  past  and  for  one  million  of 
years  to  come.  His  well-known  work  gives  the  results  of  this 
laborious  undertaking,  and  exhibits  them  in  a  graphic  form.*  At 
a  glance  it  is  evident  that  the  variations  are  both  great  and  irregu- 
lar, for  the  curve  resembles  an  exaggerated  section  of  a  series  of 
mountain  ranges.  At  the  present  time,  it  will  be  remembered,  the 
eccentricity  is  comparatively  small,  and  will  continue  to  diminish 
for  several  thousands  of  years,  so  that  even  50,000  years  hence  it 
will  not  be  much  larger  than  it  is  at  present.  Looking  backward, 
we  find  that  for  a  long  time  its  present  value  generally  has  been 
exceeded,  sometimes  very  greatly  so.  At  a  period  of  about  50,000 
years  ago  the  value  declined  for  a  time  below  the  reading  for  1800 
A.  D.,  but  the  next  300,000  years  display  a  most  unpromising  record. 
Thrice  during  this  period,  at  intervals  fairly  uniform,  the  eccen- 
tricity rises  to  a  high  figure.f  The  first  occurred  about  100,000 
years  since,  when  the  eccentricity  was  nearly  treble  its  present 
amount;  it  then  declined,  though  still  remaining  high,  the  mini- 
mum value,  which  fell  rather  less  than  50,000  years  farther  back, 
being  roughly  double  the  present  one.  A  little  after  the  end  of 
the  200,000  years'  period  it  attained  its  maximum ;  at  250,000 
years  it  fell  again  slightly  below  the  former  minimum,  but  some 
time  after  300,000  years  reached  another  maximum — that  is  to  say, 
the  eccentricity  did  not  fall  nearly  so  low  as  its  present  value,  dur- 
ing a  period  which  began  50,000  years  back,  and  lasted  for  300,000 
years,  while  it  was  extremely  high  at  the  following  (very  approxi- 
mate) dates:  100,000,  200,000,  and  300,000  B.C. — in  other  words, 
the  Glacial  epoch  might  be  regarded  as  lasting  about  300,000  years, 
and  ending  about  50,000  years  ago. 

These  are  figures  which  we  can  handle,  and,  to  some  slight 
extent,  attempt  to  check  by  the  results  of  inductive  research  in 
other  direction's.  Dr.  Croll  points  out  that  this  interval  is  suffi- 

*  Croll,  "Climate  and  Time,"  ch.  xix. 

f  The  figures  are  .0473,  .0569,  .0424,  as  against  .0168,  the  present  value.  If  we  use  the 
illustration  of  a  mountain  chain,  they  may  be  represented  as  hills  of  4730,  5690,  and  4240 
feet,  as  against  one  of  1680  feet  high. 


CLIMATAL   CHANGE:    ITS  CAUSE  AND  HISTORY.  505 

ciently  long  to  admit  of  each  hemisphere  being  affected  in  turn  by 
the  results  of  precession,  while  the  changes  are  sufficiently  slow  to 
allow  the  effects  of  a  high  eccentricity  to  be  more  than  once  miti- 
gated or  intensified.  Within  100,000  years  nearly  five  complete 
precessional  cycles  are  included,  for  in  10,500  years  a  hemisphere 
passes  from  the  condition  of  winter  in  aphelion  to  that  of  winter  in 
perihelion,  so  that  the  effects  of  a  changing  eccentricity  would  be 
intensified  or  mitigated.  Suppose,  for  example,  that  about  200,000 
years  ago,  when  the  eccentricity  had  risen  to  its  highest  value,  we 
consider  the  case  of  the  northern  hemisphere;  it  should  suffer, 
according  to  Dr.  Croll's  view,  from  a  glacial  epoch  of  exceptional 
severity,  the  winter  occurring  in  aphelion.  At  the  end  of  10,500 
years,  while  the  eccentricity  is  still  high,  but  is  decreasing,  this  sea- 
son falls  in  perihelion,  so  that  the  result  should  be  a  considerable 
improvement  in  climate.  At  the  end  of  another  10,500  years  win- 
ter again  falls  in  aphelion,  and  the  climate  should  become  more 
inclement;  but,  as  the  eccentricity  has  continued  to  diminish,  the 
one  change  to  some  extent  should  neutralize  the  other.  Similar 
conditions  should  recur,  so  far  as  precession  is  concerned,  approxi- 
mately at  the  following  periods:  179,000,  158,000,  137,000,  116,000, 
95,000  years,  while  the  eccentricity  fell  to  its  smallest  value  rather 
less  than  150,000  years  ago,  and  rose  to  its  next  highest  value  at 
about  100,000  years.  The  latter  date  corresponds  very  nearly  with 
the  quarter  point,  as  it  may  be  called,  in  the  precessional  cycle;  so 
that  any  climatal  alteration  would  be  probably  due  to  the  changed 
value  of  the  eccentricity.  But,  as  the  latter  reached  its  minimum 
rather  less  than  150,000  years  ago,  the  effect  of  precession  would 
lead,  on  the  whole,  to  a  further  amelioration  of  climate  in  this  hemi- 
sphere. This  long  period — over  250,000  years — during  which  the 
eccentricity  continued  well  above  its  present  amount,  would  give 
ample  time  for  extension  of  glaciation  in  this  hemisphere;  and  the 
precessional  movement — at  one  time  intensifying,  at  another  neu- 
tralizing the  effects  of  a  high  eccentricity — would  explain  the 
apparent  oscillation  of  temperature  exhibited  in  the  alternations  of 
bowlder  clays  and  sands,  and  the  intermingling  of  the  faunas  seem- 
ingly representative  of  rather  different  climates. 

At  first  sight  Dr.  Croll  seems  to  have  made  out  a  strong  case  in 
favor  of  placing  the  Glacial  epoch  during  this  interval  of  250,000 
years;  but  difficulties  arise  on  a  closer  study  of  the  question.  Dur- 
ing the  remainder  of  the  3,000,000  years,  for  which  the  calculation 
has  been"  made,  the  eccentricity  generally  has  ruled  considerably 


5°6  THE   STORY  OF  OUR  PLANET. 

above  its  present  value.  Only  four  times  did  it  fall  materially 
below  this;  eight  times  it  was  above  the  lowest  of  the  three 
maxima  attained  during  the  Glacial  epoch,  and  quite  as  often  very 
nearly  equal  to  the  same,  and  thrice  it  much  surpassed  the  highest 
of  them.  These  were  850,000,  2,500,000,  and  2,600,000  years  ago.* 
A  very  low  eccentricity  (.0053)  occurred  2,650,000  years  since.  If 
we  suppose  this  to  have  corresponded  with  the  warmer  part  of  the 
Eocene  period,  the  climate  of  Europe  should  have  been  seldom  bet- 
ter, and  commonly  worse,  than  at  present,  while  at  least  one  very 
severe  glacial  epoch  should  have  occurred  in  the  Eocene  itself. 
Notwithstanding  the  possible  significance  of  the  singular  bowlders 
and  breccias -in  the  flysch,  the  fauna  and  flora  of  the  Eocene  seern 
irreconcilable  with  the  hypothesis  of  the  continuance  of  a  cold 
climate  for  any  considerable  time ;  and  the  general  impression  con- 
veyed by  palaeontology,  throughout  the  greater  part  of  the  Tertiary 
period,  is  totally  opposed  to  the  existence  of  conditions  which  seem 
to  follow  from  the  record  itself,  when  interpreted  in  accordance 
with  Dr.  Croll's  own  principles.  Of  course,  if  geological  time  be 
extended  far  beyond  the  limit  of  a  hundred  million  years,  the  whole 
of  the  record  from  which  the  calculation  was  made  might  be 
regarded  as  covering  only  the  later  and  colder  portion  of  the  Ter- 
tiary era,  but  then  other  difficulties  will  have  to  be  confronted. 
The  date  assigned  to  the  Glacial  epoch  by  these  calculations  and 
inferences — viz.,  from  about  350,000  to  50,000  years  ago — may  be 
checked,  to  some  extent,  by  an  endeavor  to  estimate  the  time 
which  has  elapsed  since  the  retreat  of  the  ice,  from  the  amount  of 
erosion  which  has  subsequently  taken  place.  On  this  point,  as 
might  be  expected,  great  diversity  of  opinion  exists.  Certain 
American  geologists — from  observations  at  various  places,  such  as 
the  shores  of  Lake  Michigan,  some  gorges  on  the  Mississippi,  the 
Falls  of  St.  Anthony,  sundry  tributaries  to  Lake  Erie,  and  the  Falls 
of  Niagaraf— place  the  melting  of  the  ice  at  not  more  than  about 
eight  thousand  years  back.  This  date,  as  already  said,  seems 
improbably  recent ;  but  there  is  evidence  at  any  rate  sufficient  to 
make  us  cautious  in  claiming  a  very  remote  date  for  the  Glacial 
epoch,  so  that  we  can  hardly  venture  to  look  beyond  the  one  which, 
as  stated  above,  corresponds  with  the  last  triple  group  of  high 
eccentricities. 

*When  the  eccentricities  are  respectively  .0747,  .0721,  and  .0660. 

f  See  Wright,  "  The  Ice  Age  in  North  America,"   p.  549.     The  general  aspect  of  the 
valleys  in  the  Alps  indicates  but  little  change  since  the  ice  left  them. 


CLIMATAL  CHANGE':    ITS  CAUSE  AND  HISTORY.  507 

There  is  yet  another  difficulty,  at  which  indeed  we  have  already 
hinted — namely,  that  if  this  calculation  allows  any  inference  to  be 
drawn  as  to  the  history  of  the  earth  in  ages  still  more  remote,  its 
climate,  on  the  whole,  ought  to  have  been  less  genial  than  at 
present,  and  glacial  epochs  to  have  occurred  rather  frequently.  No 
doubt  it  is  extremely  difficult  to  arrive  at  any  conclusions  on  these 
points,  and  especially  on  the  former;  but,  as  already  said,  such 
evdience  as  we  possess  tends  in  the  opposite  direction.  Dr.  Croll, 
it  is  true,  has  endeavored  to  show  that  indications  of  glacial  epochs 
are  not  unfrequent  among  the  stratified  rocks;  but  most  of  the 
cases  which  he  brings  forward  appear  to  me  to  rest  on  very  slender 
evidence,  and  his  efforts  to  account  for  the  absence  of  any  of  a 
more  convincing  character  to  be  far  from  successful. 

So  the  question  of  the  date  of  the  Glacial  epoch  seems,  in  the 
present  stage  of  our  knowledge,  to  be  hardly  more  capable  of  solu- 
tion than  that  of  its  cause.  It  may  be  rather  humiliating  to  make 
the  confession;  but  in  these  problems,  as  in  so  many  others,  we 
must  be  content  to  give  a  hesitating  answer,  to  state  the  facts  and 
indicate  the  directions  in  which  they  tend,  and  to  leave  the  com- 
plete solution — if,  indeed,  that  be  ever  accomplished — to  a  future 
generation,  which  will  have  added  to  our  knowledge  and  learned 
from  our  mistakes. 


CHAPTER  IV. 

THE   DISTRIBUTION   AND   THE   DESCENT   OF   LIFE. 

THE  problem  of  the  distribution  of  life  on  the  surface  of  the 
globe  is  so  difficult  and  intricate  that  if  anything  more  than  the 
merest  outline  were  attempted,  this  book  would  be  enlarged  beyond 
all  reasonable  limits.  Perhaps  a  general  idea  of  the  leading  prin- 
ciples by  which  it  appears  to  be  regulated  will  be  most  easily 
obtained  from  a  brief  summary  of  a  few  important  facts  which  are 
afforded  by  the  study  of  the  flora  and  fauna  of  one  or  two  districts. 
We  may  take,  as  the  first  example,  the  British  Isles.  Their  flora  is 
closely  related,  on  the  whole,  to  that  of  France  and  Germany ;  the 
distinctions  are  hardly  more  than  varietal,  but  the  number  of 
species  is  smaller.  It  is  accordingly  inferred  that  till  a  compara- 
tively late  age  Britain  was  connected  with  Western  Europe,  and 
this  is  fully  borne  out  by  geological  evidence.  But  one  or  two 
local  peculiarities  are  exhibited  by  the  flora  which  call  for  explana- 
tion. For  instance,  a  small  group  of  plants  flourishes  in  the  south- 
west of  Ireland — such  as  the  strawberry  tree  (Arbutus  nnedd),  the 
Mediterranean  heath  (Erica  mediterranea),  the  London  pride 
(Saxifraga  umbrosa),  and  two  or  three  other  species  of  that  genus — 
which  now  are  not  found  elsewhere  north  of  the  Pyrenees  and  Alps.* 
Again,  in  parts  of  Cornwall  and  Devon  a  second  group  of  plants  is 
found — including  the  tamarisk  ( Tamarix gallica),  the  autumn  squill 
(Scilla  autumnalis),  the  Cornish  heath  (Erica  vagans),  and  the  cili- 
ated heath  (E.  ciliaris) — for  which  we  must  generally  go  to  the 
southern  or  western  parts  of  France.  A  third  group  of  plants 
clusters  around  the  mountain  summits,  which  thus  may  be  com- 
pared to  botanical  islands.  These  plants — such  as  the  moss 
campion  (Silene  acaulis),  the  mountain  saxifrage  (Saxifraga  oppos- 
itifolid),  the  dwarf  azalea  (Azalea  procumbens),  the  snow  gentian 
(Gentiana  nivalis),  etc. — are  found  in  abundance  on  the  Pyrenees, 
the  Alps,  and  the  greater  part  of  Norway,  some  being  confined  to 

*  There  are  also  two  American  species,  one  of  which — the  pipe-wort  (Eriocaulon  septan- 
gulare) — is  found  in  the  Hebrides,  as  well  as  the  west  of  Ireland. 

508 


THE  DISTRIBUTION  AND    THE  DESCENT  OF  LIFE.  509 

the  last-named  region.  Plants  also,  strictly  Scandinavian,  are  more 
numerous  in  the  northern  than  in  the  southern  parts  of  Britain ; 
for  example,  Primula  scotica  is  limited  to  the  northern  shores  of 
Scotland;  Cornus  suecica,  Trientalis  enropcea,  and  Rubus  chamcz- 
morus  get  down  as  far  as  the  Yorkshire  hills,  but  only  the  last  to 
the  mountains  of  Wales.  On  consideration  of  the  circumstances 
associated  with  the  distribution  of  this  last  group,  the  conclusion 
seems  warranted  that  it  contains  representatives  of  the  plants  which 
occupied  the  British  Isles  and  the  adjacent  parts  of  Europe  at  or 
about  the  time  of  the  Glacial  epoch ;  these,  as  the  climate  became 
less  severe,  would  find  the  lowland  regions  unsuitably  warm  and 
would  retreat  into  the  uplands.  On  the  lower  hills  they  would  be, 
as  it  were,  drowned  by  the  advancing  waves  of  heat,  but  in  the 
more  mountainous  districts  some  would  find  camps  of  refuge. 
Obviously  the  safest  and  the  most  general  line  of  retreat  would  be 
toward  the  north,  which  accounts  for  the  British  plants  having  a 
closer  connection  with  the  Scandinavian  flora  than  with  the  Alpine. 
From  the  north  these  plants  probably  came  as  invaders  when  the 
cold  was  increasing;  to  it  they  were  driven  back  "like  a  beaten 
army"  when  the  climate  again  became  warmer.  But  how  are  the 
other  two  insulated  groups  of  plants  to  be  explained?  Some  have 
considered  them  indicative  of  a  direct  land  connection,  in  very  late 
geological  times,  between  Southern  Ireland,  Cornwall,  and  the 
Spanish  peninsula.  So  far  as  regards  the  plants  common  to  the 
southwest  of  England  and  the  Breton  promontory  or  the  Channel 
Islands,  this  is  a  possible  explanation,  but  it  can  hardly  apply  to 
those  in  the  first  group,  for  the  great  depth  of  the  Bay  of  Biscay 
and  of  the  sea  between  Ireland  and  Portugal  makes  it  improbable 
that  these  were  directly  linked  together  by  a  land  mass  at  so  recent 
a  date.  I  am  accordingly  disposed  to  regard  the  latter  group,  if 
not  both  of  them,  as  survivors  of  the  flora  which  occupied  Western 
Europe  in  Miocene  and  Pliocene  times,  and  contrived  to  survive 
the  Glacial  cold,  in  certain  more  genial  nooks  on  the  border  of  the 
Atlantic,  as  persons  of  delicate  constitution  at  the  present  day 
betake  themselves  to  the  sunny  shore  of  the  Riviera. 

But  the  ordinary  British  flora  is  undoubtedly  an  immigrant  from 
the  mainland  of  Europe.  It  contains  fewer  species,  and  hardly  any 
that  are  peculiar.*  The  same  may  be  said  of  the  fauna.  About  2 

*  According  to  the  late  H.  C.  Watson,  there  is  no  plant  peculur  to  the  British  Isles 
which  can  be  regarded  as  more  than  a  variety  or,  at  most,  a  sub-species. 


510  THE   STORY  OF  OUR  PLANET. 

species  of  mollusca,  72  species  of  coleoptera,  69  of  lepidoptera,  15 
of  fishes,  and  3  of  birds  are  peculiar  to  the  British  Isles,  but  most 
of  them  are  closely  allied  to  continental  forms.  For  instance,  the 
red  grouse  (Lagopus  scoticus),  which  is  the  most  markedly  distinct 
bird  in  these  islands,  is  nearly  related  to  the  willow  grouse  of  Scan- 
dinavia. As  Mr.  Wallace  points  out,*  the  evidence  of  the  mam- 
mals, reptiles,  and  amphibia  is  remarkably  convincing.  In  Ger- 
many are  90  species  of  mammals;  in  Britain,  40;  in  Ireland,  22.  In 
Belgium  the  reptiles  and  amphibians  number  22  species;  in  Britain, 
13;  in  Ireland,  4.  These  statistics  lead  to  three  conclusions:  one, 
that  the  fauna  spread  gradually  from  the  east  or  southeast  into 
these  islands;  the  second,  that  Ireland  was  separated  from  Great 
Britain  while  the  latter  was  still  connected  with  Europe;  the  third, 
that  the  differences  of  environment  have  produced  some  slight 
effects  on  certain  of  the  forms  thus  insulated. 

We  pass  on  to  the  Azores.  This  group  of  islands — nine  in  num- 
ber— extends,  from  the  southeast  to  the  northwest,  over  a  distance 
of  nearly  400  miles,  the  nearest  being  not  quite  900  miles  away 
from  the  Portuguese  coast,  and  separated  by  a  part  of  the  ocean 
2500  fathoms  deep.  The  following  is  a  brief  summary  of  Mr.  Wal- 
lace's remarks:  There  are  no  indigenous  land  mammals,  no  amphib- 
ians, no  snake,  lizard,  frog,  or  fresh-water  fish ;  in  a  word,  no  terres- 
trial vertebrates  ;f  but  winged  creatures,  such  as  birds  and  insects, 
are  abundant;  and  there  is  even  a  flying  mammal — a  small  Euro- 
pean bat.  The  birds  are  53  in  number,  mostly  species  that  are 
strong  on  the  wing.  Of  the  land  birds,  18  in  number,  all  except 
three  are  common  in  Europe  or  North  Africa.  Of  these,  two 
inhabit  Madeira:}:  and  the  Canary  Islands;  and  one,  the  Azorean 
bullfinch,  is  peculiar  to  the  Azores.  The  beetles  number,  at  pres- 
ent, 212,  of  which  175  are  European ;  but  probably  only  74  are  really 
indigenous;  36  species  are  not  European,  of  which  19  are  natives 
of  Madeira  or  the  Canaries,  and  are  altogether  peculiar  to  the 
Azores.  Of  the  land  shells  there  are  69  species,  of  which  37  are 
common  to  Europe  or  to  the  other  Atlantic  isles,  while  32  are 
peculiar,  though  almost  all  are  distinctly  allied  to  European  types. 
The  majority  of  these  shells,  especially  the  peculiar  forms,  are  very 
small,  and  many  of  them  date  back  to  beyond  the  Glacial  epoch. 

*  "  Island  Life,"  p.  319. 

t  There  are  a  few  mammals,  some  fish,  and  a  lizard,  but  there  are  reasons  to  believe 
these  have  been  introduced. — "  Island  Life,"  p.  240. 
|  This  is  more  than   550  miles  away. 


THE  DISTRIBUTION  AND    THE  DESCENT  OF  LIFE.  511 

Of  the  plants  (480  species)  no  less  than  440  are  found  also  in 
Europe,  Madeira,  or  the  Canary  Islands;  while  40  are  peculiar  to 
the  Azores,  but  are  more  or  less  closely  allied  to  European  species. 
As  the  Azores  are  entirely  composed  of  volcanic  rocks,  and  are  sur- 
rounded on  all  sides  by  a  wide  expanse  of  deep  ocean,  it  is  improb- 
able that  they  were  ever  connected  with  any  continental  lajid. 
The  statistics  quoted  above  warrant  the  conclusion  that  the  fauna 
and  flora  are  all  colonists,  stragglers  from  the  adjacent  mainland 
and  islands,  which  have  been  wafted  by  the  winds  or  drifted  by  the 
ocean  currents,  but  that  sundry  of  them  have  been  settled  there 
long  enough  to  be  so  far  modified  as  to  be  readily  distinguishable 
from  their  allies  on  the  mainland.  The  latter  also  may  have  pos- 
sibly diverged  slightly  from  the  parent  stems.  The  insulation,  in 
short  (if  we  may  so  call  it),  is  more  complete,  and  of  more  ancient 
date  than  in  the  case  of  the  British  Isles. 

We  must  refer  to  Mr.  Wallace's  most  valuable  work  on  "Island 
Life"  for  other  instances  of  the  same  kind,  and  conclude  by  briefly 
noticing  the  case  of  Australia  and  the  islands  which  are  usually 
associated  with  it  in  the  same  zoologcial  province.  This,  according 
to  Mr.  Wallace,*  is  "the  great  insular  region  of  the  earth.  .  .  Its 
central  and  most  important  masses  consist  of  Australia  and  New 
Guinea,  in  which  the  main  features  of  the  region  are  fully  devel- 
oped. To  the  northwest  it  extends  to  Celebes,  in  which  a  large 
proportion  of  the  Australian  characters  have  disappeared,  while 
Oriental  types  are  mingled  with  them  to  such  an  extent  that  it  is 
rather  difficult  to  determine  where  to  locate  it.  To  the  southeast 
it  includes  New  Zealand,  which  is  in  some  respects  so  peculiar  that 
it  has  even  been  proposed  to  constitute  it  a  distinct  region.  On 
the  east  it  embraces  the  whole  of  Oceanica  to  the  Marquesas  and 
Sandwich  Islands,  whose  very  scanty  and  often  peculiar  fauna  must 
be  affiliated  to  the  general  Australian  type."  Zoologically,  the 
Australian  region  is  different  from  all  the  rest  of  the  globe  by  the 
entire  absence  of  all  the  orders  of  non-aquatic  mammalia  that 
abound  in  the  Old  World,  except  the  bats  (which  are  winged)  and 
one  family  of  rodents,  the  Muridce  (rats  and  mice),  and  the  repre- 
sentatives of  these  are  small  or  moderate  in  size.  The  other  mam- 
mals, except  two  monotremesf — the  lowest  in  the  scale  of  develop- 

*  "  Geographical  Distribution  of  Animals,"  ch.  xiii. 

f  The  Ornithorhynchus  and  Echidna,  "  probably  the  descendants  of  some  of  those 
earlier  developments  of  mammalian  life  which  in  every  other  part  of  the  globe  have  long 
been  extinct." 


512  THE   STORY  OF  OUR   PLANET. 

ment — are  all  marsupials,  which  are  wonderfully  developed  in 
Australia,  and  exist  in  the  most  diversified  forms.  "Some  are 
carniverous,  some  herbivorous,  some  arboreal,  others  terrestrial. 
There  are  insect-eaters,  root-gnawers,  fruit-eaters,  honey-eaters,  leaf- 
or  grass-feeders.  Some  resemble  wolves,  others  marmots,  weasels, 
squirrels,  flying  squirrels,  dormice,  or  jerboas.  .  .  Yet  they  all 
possess  common  peculiarities  of  structure  and  habits,  which  show 
that  they  are  members  of  one  stock,  and  have  no  real  affinity  with 
the  Old  World  forms  which  they  often  outwardly  resemble.  .  . 
The  ornithological  features  of  the  Australian  regions  are  almost  as 
remarkable  as  those  presented  by  its  mammalian  fauna,  and  from 
the  fuller  development  attained  by  the  aerial  class  of  birds,  much 
more  varied  and  interesting.  None  of  the  other  regions  of  the 
earth  can  offer  us  so  many  families  with  special  points  of  interest 
in  structure  or  habits  or  general  relations.  The  paradise  birds,  the 
honey-suckers,  the  brush-tongued  paroquets,  the  mound-builders, 
and  the  cassowaries — all  strictly  peculiar  to  the  region — place  it  in 
the  first  rank  for  the  variety,  singularity,  and  interest  of  its  birds." 
The  reptiles,  amphibians,  fresh-water  fish,  insects,  and  terrestrial 
mollusca  exhibit  peculiarities,  but  are  less  distinctive,  on  the  whole, 
than  the  mammals  and  the  birds ;  while  the  plants,  notwithstand- 
ing the  existence  of  several  very  marked  forms,  are  sufficiently 
allied  to  those  of  Asia  to  be  combined  in  one  botanical  region.* 
Mr.  Wallace,f  several  years  since,  called  attention  to  the  remarkable 
proximity  in  one  part  of  the  Oriental  and  Australasian  zoological 
provinces,  and  the  short  separation  between  them.  To  the  east  of 
Java  a  strait  of  the  sea  about  fifteen  miles  wide  separates  the 
islands  of  Bali  and  Lombok,  yet  the  fauna  of  the  one  is  distinctly 
Oriental,  of  the  other  no  less  distinctly  Australasian.  Mr.  Wallace, 
after  a  discussion  of  all  the  evidence  which  he  could  obtain,  comes 
to  the  conclusion  that  most  probably  the  Australian  region  has  not 
been  connected  with  the  northern  continent  since  an  early  date  in 
the  Secondary  era,  and  since  that  time  has  gone  on  developing  its 
mammalian  fauna  into  the  existing  races.  Still  the  variations  in 
the  disposition  of  sea  and  land  within  this  region  have  been  many. 
For  instance,  New  Zealand,  as  he  believes,  received  its  flora  and 
fauna  from  Eastern  Australia  at  a  time — probably  toward  the  end 
of  the  Secondary  era — when  the  latter  was  divided  by  sea  from 


*See  Blanford,  Presidential  Address  to  the  Geological  Society,  1890,  p.  82  (Proceedings). 
f  "  The  Malay  Archipelago,"  ch.  i. 


THE   DISTRIBUTION  AND    THE  DESCENT  OF  LIFE. 


513 


Western  Australia,  and  "the  characteristic  marsupial  and  mono- 
treme  fauna,  with  all  the  peculiar  temperate  flora  of  Australia,  was 
confined  to  the  western  island." 

Many  like  instances  are  given  by  Darwin,  Wallace,  and  other 
writers  on  the  questions  connected  with  the  distribution  of  life.  The 
evidence  collected  leads  to  the  following  general  conclusion :  That 
the  fauna  and  flora  of  an  island  are  always  related  to  those  of  some 


FlG.   169. — MAP   SHOWING  HOW   THE   DEEP   NARROW   STRAIT  BETWEEN    BALI   AND 
LOMBOK    SEPARATES   THE    AUSTRALASIAN    FROM    THE    INDO-MALAYAN  FAUNA. 


neighboring  land,  and  that  each  member  of  an  island  group  is  con- 
nected with  the  others,  and  directly  or  indirectly  with  the  nearest 
mainland. 

If  there  are  links  with  more  than  one  continent,  these  will  be  the 
strongest  in  the  direction  of  the  place  from  which  migration  is  most 
easy.  The  spread  of  a  land  flora  and  fauna  is  mainly  impeded  by 
seas  or  (to  a  less  degree)  by  mountain  chains  and  deserts ;  that  of  a 
marine  flora  and  fauna  by  land  barriers,  and  to  no  small  degree  by 
great  variations  in  depths.  The  more  marked  the  divergence 
between  an  insular  and  mainland  flora  or  fauna,  the  more  remote 
the  date  of  separation.  The  conclusion  seems  irresistible  that  each 
variety  or  each  species  has  been  differentiated  from  its  nearest  ally 
or  allies  by  the  effect  of  its  altered  conditions  of  life;  or,  in  some 


5M  THE    STORY  OF  OUR  PLANET. 

cases,  that  their  distinctions  are  due  to  a  divergence  on  both  sides 
from  a  common  ancestral  type. 

So  far  as  regards  most  insular  and  some  continental  floras  and 
faunas,  a  derivative  origin  and  a  modification  by  alteration  of  cir- 
cumstances may  be  regarded  as  established  by  evidence  which  it 
would  be  very  difficult  to  refute.  When  we  come  to  the  great 
question  of  the  origin  of  species,  which  since  the  publication  of  Dar- 
win's classic  work  has  influenced  and  directed  the  studies  of  so 
many  naturalists,  we  may  not  venture  at  present  to  use  quite  so 
strong  a  phrase ;  but  we  cannot  deny  that,  although  the  existence 
of  some  difficulties  must  be  frankly  admitted,  the  evidence  in  its 
favor  has  been  so  much  strengthened  during  the  last  thirty  years 
that  the  general  accuracy  of  the  leading  idea — which  occurred  inde- 
pendently to  Darwin  and  Wallace — can  hardly  be  doubted.  There 
may  be  factors  at  work  in  causing  changes  other  than  those 
included  in  the  term  "Natural  Selection."  It  may  be  that  prog- 
ress is  only  possible  in  certain  fairly  definite  directions:  that  in 
consequence  of  innate  tendencies,  as  they  may  be  called,  limits 
exist,  within  which  only  (however  wide  they  may  be)  variation 
is  possible;  in  other  words,  the  whole  truth  in  regard  to  this  sub- 
ject may  not  yet  have  been  discovered.  But  we  cannot  deny,  if 
the  matter  be.  viewed  without  prejudice,  that  these  leaders  in 
science  have  arrived  at  a  most  important  truth,  and  have  come  much 
nearer  to  a  complete  solution  of  the  mystery  than  those  who  main- 
tained any  form  of  the  hypothesis  of  special  creation. 

Allowance  must  be  made  for  the  imperfection  of  the  geological 
record,  to  which  attention  has  already  been  called,*  but,  notwith- 
standing this,  it  must  be  admitted  that  the  flora  and  fauna  of  any 
district,  whether  they  be  tenants  of  the  land  or  of  the  sea,  are  the 
descendants  of  their  predecessors  in  the  same  region.  As  they  are 
traced  somewhat  further  back,  evidence  is  frequently  obtained  of 
dispersions  in  different  directions  and  migrations  by  paths  which  are 
sometimes  no  longer  practicable.  The  type  is  obviously  the  out- 
come of  its  environment,  and  the  environment,  regarded  as  a  whole, 
may  be  termed  a  function  of  several  variables,  and  is  very  liable  to 
change.  The  geography  of  the  earth  is  modified,  as  we  have  seen, 
by  the  action  of  forces  from  within  and  from  without ;  by  these, 
and  possibly  by  influences  yet  more  remote  in  their  origin,  climate 
has  been  altered,  and  the  other  circumstances  may  be  made  so 

*  Pp.  332-334- 


THE  DISTRIBUTION  AND    THE  DESCENT    OF  LIFE.  51$ 

different  as  to  become  either  very  favorable  or  very  unfavorable  to 
the  variation  or  even  to  the  existence  of  particular  types  of  living 
creatures.  Apart  from  such  obvious  cases  as  the  replacement  of 
sea  by  land  or  land  by  sea,  there  are  many  less  startling  which  pro- 
duce effects  often  far  from  unimportant.  There  are,  for  example, 
marked  differences  in  the  flora  even  of  any  one  country,  dependent 
on  the  soil  and  the  situation  of  the  district.  In  the  British  Islands 
one  group  of  plants  characterizes  the  marshland,  another  the 
sandy  heaths,  a  third  the  chalk  hills,  and  so  on ;  and  with  these 
differences  in  the  fauna  are  more  or  less  closely  connected.  If  a 
food  plant  disappears,  the  animal  which  is  dependent  on  it  is  in  a 
"parlous"  condition ;  it  must  seek  "fresh  woods  and  pastures  new," 
or  it  must  perish;  and  when  any  living  creature  begins  to  travel,  or 
in  any  way  to  alter  its  habits  of  life,  as  both  the  sum  total  and  the 
constituents  of  its  environment  are  changed,  modification  becomes 
inevitable. 

But  for  a  full  discussion  of  this  subject  we  must  refer  the  reader 
to  the  classic  columns  already  mentioned,  and  content  ourselves 
with  calling  attention  to  three  topics  which  seem  of  special  interest 
as  bearing  on  this  general  question.  The  first  is  the  direct  evidence 
of  modification,  due  to  altered  conditions,  which  is  exhibited  when 
the  line  of  descent  of  some  living  creature  is  traced  back;  the 
second,  the  exhaustion  which  sometimes  seems  to  follow  an  over- 
indulgence, as  it  may  be  called,  in  modification ;  and  the  third 
relates  to  the  influence  which  the  human  race  has  exercised  in  alter- 
ing the  conditions  of  life  on  the  globe. 

As  regards  the  first :  changes  in  the  conditions  of  life  lead  to  the 
development  of  organs  which  are  constantly  in  requisition  and  to 
the  abortion  of  those  which  fall  into  disuse.  It  will  suffice  to  notice 
the  latter  case,  because  the  existence  of  an  aborted  organ  bears 
more  directly  upon  the  rival  hypotheses  of  special  creation  and  of 
evolution.  As  an  example  it  is  difficult  to  find  a  better  instance 
than  that  so  often  quoted — the  genealogy  of  the  horse.  The  foot 
of  the  living  group — of  which  Equus  caballus  is  the  type — consists 
of  one  large  digit  (No.  III.,  E),  on  either  side  of  which  is  a  thin  long 
bone  (the  splint  bone).  This  animal  first  appears  at  the  top  of  the 
Pliocene  deposits  (in  India),  and  among  the  earliest  forms  some 
modifications  are  taking  place,  especially  in  the  molar  teeth,  which 
bring  the  genus  very  near  to  a  Pliocene  genus,  called  Hipparion, 
found  in  both  the  New  World  and  the  Old,  where  the  splint  bones  are 
replaced  (D)  by  two  small  but  fairly  complete  digits  (No.  II.,  IV.). 


THE   STORY  OF  OUR  PLANET. 


In  C  we  have  the  form  of  the  foot  in  Anckit her  turn,  an  animal 
belonging  to  the  Miocene  period,  where  the  side  digits  are  larger 
(II.,  IV.)  compared  with  the  middle  one  (III-);  an<^  then  we  are  led 
by  some  transitional  Upper  Eocene  forms  resembling  Palaothcrium 
(B)  to  Hyracotherium  of  the  Lower  Eocene,  where  the  forefoot, 
which  is  like  that  of  a  tapir  (A)  has  four  complete  digits  (as  marked), 


P'IG.  170. — VARIOUS  FORMS  OF  FEET,  ILLUSTRATING  DEVELOPMENT  OF  ONE  DIGIT 
AND  ABORTION  OF  OTHERS. 

A,  Tapir ;  B,  Palaeotherium  ;  c,  Anchitherium  ;  D,  Hipparion  ;  K,   Horse. 

and  an  allied  creature  (Eohippus)  has  even  rudimental  indications  of 
the  fifth  digit.  Finally  the  earliest  stage  of  the  series  is  formed  by 
an  animal  (Phenacodus)  of  the  Lowest  Eocene  of  North  Amercia,  in 
which  there  are  five  digits  to  each  foot.  Mr.  Lydekker,  on  whose 
authority  these  statements  are  given,  calls  attention  to  a  remarka- 
ble circumstance  in  the  line  of  evolution  culminating  in  the  modern 
horse.  "A  parallel  series  of  generically  identical  or  closely  allied 
forms  occur  in  the  Tertiaries  of  both  Europe  and  North  America, 
from  which  it  has  been  suggested  that  in  both  continents  a  parallel 
development  of  the  same  genera  h,as  simultaneously  taken  place — 
/.  e.,  that  in  both  regions  Anchitherium  has  given  rise  to  Hipparion, 
and  Hipparion  or  an  allied  type  to  Equus.  Now  seeing  it  is  evi- 
dent that  in  the  case  of  species  of  a  single  genus  the  evolution  has 
taken  place  in  separate  lines — that  is  to  say,  the  existing  Indian 
species  of  Cants  are  probably  derived  directly  from  the  Pliocene 


THE  DISTRIBUTION  AND    THE   DESCENT  OF  LIFE.  51? 

forms  of  the  same  region,  and  the  Brazilian  species  of  that  genus 
have  their  predecessors  in  the  cave  epoch  of  that  country — there 
appears  no  logical  reason  for  refusing  to  admit  an  analogous  parallel 
evolution  in  the  case  of  genera,  and  there  is  accordingly  a  con- 
siderable probability  that  the  hypothesis  may  be  a  true  one."* 

The  genealogy  of  other  forms,  both  vertebrate  and  invertebrate, 
has  been  traced,-  one  or  two  cases  of  which  have  been  incidentally 
noticed  elsewhere  in  this  book.  The  evidence,  on  the  whole,  is  so 
strong  that  even  those  palaeontologists  who  are  still  indisposed 
wholly  to  abandon  the  old  idea  of  a  special  creation  of  certain 
original  types  are  compelled  to  admit  that  very  great  variation  has 
occurred,  and  that  not  a  few  groups  of  living  creatures  must  have 
diverged  from  some  primary  and  ancestral  form.  They  would  also 
admit  that  these  exhibit  on  the  whole  a  progress  from  the  general 
to  the  specialized,  from  the  more  embryonic  to  the  more  highly 
developed  in  structure,  while  the  disused  organs  become  abortive. 

In  the  second  place,  there  is  some  evidence  to  show  that  after  an 
assemblage  of  living  creatures  has  attained  in  the  process  of  evolu- 
tion to  a  certain  stage  of  specialization,  such  as  would  be  expressed 
in  classification  by  placing  the  members  in  the  same  genus  or  close 
association  of  genera,  their  original  stock  of  vital  energy,  if  the 
phrase  be  permissible,  seems  to  be  so  far  limited  as  to  be  liable  to 
exhaustion.  As  a  general  rule  a  genus,  family,  or  even  order,  when 
it  first  appears,  is  not  for  a  time  very  abundant,  as  though  it  had  to 
fight  for  its  existence  against  somewhat  adverse  conditions.  Some- 
times, indeed,  it  fails  to  make  good  its  footing.  It  continues  for  a 
while,  but  is  never  numerous,  either  specifically  or  even  individually. 
Finally  it  disappears,  and  may  be  counted  among  Nature's  failures.f 
Other  groups,  however,  win  their  way,  species  and  even  genera 
becoming  numerous,  and  the  individuals  in  them  abundant.  These, 
after  a  period  of  prosperity,  sometimes  fairly  prolonged,  seem  to 
feel  the  advance  of  senile  debility;  they  dwindle,  and  at  last  either 
totally  disappear  from  the  earth  or  are  represented  by  descendants 
few  and  insignificant.  Of  such  a  "decline  and  fall,"  which  has  its 
parallels  in  the  history  of  man,  instances  are  numerous.  The  trilo- 
bites  had  already  begun  their  existence  when  the  earliest  fossil- 
iferous  rocks  were  deposited.  They  increase  through  the  Cambrian 
and  Ordovician  systems,  reaching  a  maixmum  in  the  Bala  group, 


*  Nicholson  and  Lydekker,  "  Manual  of  Palaeontology,"  p.  1363.  - 

f  Such,  for  example,  were  the  Cystoidea  and  Blastoidea  in  the  Primary  era. 


5^8  THE   STORY  OF  OUR  PLANET. 

and  then  gradually  decrease,  until,  in  the  course  of  the  Carbon- 
iferous period,  they  totally  disappear.  The  genus  Trigonia  among 
the  ordinary  bivalve  mollusca,  and  Terebratula*  with  its  nearest 
relations,  were  very  abundant  during  the  Secondary  era.  Since 
then  they  have  waned,  and  now  have  but  a  few  representatives. 
The  Belemnites  also  prospered  through  the  greater  part  of  the  same 
era,  and  then  rather  quickly  disappeared.  Yet  more  remarkable  is 
the  case  of  the  family  of  the  Ammonitidae,  which  also  appeared  in 
Europe  at  the  beginning  of  this  era,  and  established  themselves  in 
Britain  almost  step  by  step  with  the  advancing  sea.  They  were 
represented  for  a  long  time  by  a  considerable  number  of  species, 
and  frequently  were  individually  very  abundant.  Then,  toward  the 
close  of  the  era,  their  power  of  variation  seems  to  be  much  more 
conspicuously  exhibited.  It  appears  as  though  in  a  struggle  either 
for  predominance  or  against  conditions  which  it  was  felt  were 
becoming  unfavorable,  they  attempted  to  grow  after  many  and  often 
very  diverse  typesf — then  their  vitality,  almost  suddenly,  becomes 
exhausted,  and  the  whole  family  vanishes  from  the  earth. 

Lastly,  the  results  which  have  been  produced  by  man  himself 
furnish  us  with  an  object  lesson  illustrative  of  the  changes  which 
may  have  occurred  in  past  ages  during  the  "struggle  for  existence." 
In  his  case  too  there  must  have  been  danger  for  a  time,  lest  the 
"beasts  of  the  field"  should  prevail  over  him ;  but  as  he  drew  wider 
apart  from  them  by  progress  in  civilization,  more  destructive  instru- 
ments were  substituted  for  the  first  rude  weapons  of  the  savage, 
and  he  became  the  destroyer  of  species  after  species.  Without 
entering  upon  the  more  debatable  question  of  the  causes  which 
have  been  destructive  to  the  great  mammals  which  were  contempo- 
raneous with  palaeolithic  man — such  as  the  mammoth,  the  woolly 
rhinoceros,  the  Irish  elk,  and  the  like — we  may  point  to  the  changes 
which  have  occurred  in  historic  times.  Many  of  these  have  been 
already  mentioned,  but  even  .this  century  has  seen  some  changes. 
The  drainage  of  the  Fens  destroyed  the  Great  Copper  butterfly 
(Lyccena  dispar],  and  from  some  unknown  cause  the  Mazarine  Blue 
(Polyommatus  acts)  has  also  perished.  During  the  same  period  the 
wildcat,  the  marten,  the  polecat,  the  badger,  with  may  other  ani- 
mals and  some  plants,  have  become  rarities  in  Britain ;  and  in  many 
parts  of  Africa,  Asia,  and  North  America  both  big  game  and  the 
larger  carnivora  have  become  more  and  more  scarce. 

*  This  genus  first  appears  at  a  considerably  earlier  date, 
f  Pp.  435,  436. 


THE  DISTRIBUTION' AND    THE  DESCENT  OF  LIFE.  519 

The  lists  of  extinct  and  disappearing  animals  might  have  been 
readily  increased,  but  the  instances  quoted  may  suffice  to  show  what 
changes  have  been  wrought  in  the  fauna  of  the  globe  by  man's 
appetite  for  flesh  or  by  his  passion  for  the  chase.  The  effects  of 
these  are  far  reaching.  The  destruction  of  carnivorous  animals 
removes  enemies  to  animals  commonly  herbivorous.  The  destruc- 
tion of  the  latter  alters  the  balance  of  forces  in  the  vegetable  world. 
At  St.  Helena,  we  are  told,  the  forests  on  the  hills  have  been  almost 
destroyed  by  the  goats  turned  loose  from  vessels;  the  sparrow  in 
more  than  one  part  of  the  world,  the  rabbit  in  Australia,  show  that 
man's  efforts  to  modify  the  course  of  Nature  for  his  own  advantage 
are  not  always  attended  with  success.  If  keepers  had  refrained 
from  harrying  the  Little  Owls,  the  farmers  in  Scotland  most  prob- 
ably would  not  have  been,  as  of  late,  plagued  by  voles. 

But  the  results  of  man's  interference  appear  yet  more  conspicuous 
when  he  has  operated  directly  on  the  vegetable  world.  The  neces- 
sity of  clearing  the  land  for  cultivation,  or  the  greed  of  gold,  causes 
the  wholesale  destruction  of  forests.  By  this  not  only  is  the  rain- 
fall affected,  but  also,  when  the  shower  falls,  the  water,  instead  of 
sinking  quietly  into  the  ground,  collects  into  runlets  and  quickly 
tears  away  the  soil,  now  unprotected  by  the  leaves  and  no  longer 
bound  together  by  the  roots  of  trees.  Torrents  of  mud  and  gravel 
go  raging  down  the  ravines,  choking  the  channels  of  the  lowland 
rivers  and  flooding  the  plains  with  the  debris  of  the  mountains. 
Reclus,  in  the  book  from  which  we  have  more  than  once  quoted, 
draws  a  vivid  picture  of  the  ravages  which  have  been  initiated  by 
man.*  "When  the  forests  are  gone,  great  furrows  of  erosion  may 
be  noticed  opening  out  at  intervals  on  the  slopes;  these  furrows 
often  correspond  to  ravines  situated  on  the  other  side  of  the  moun- 
tain,  and  in  a  comparatively  short  space  of  time  they  ultimately 
sever  the  ridge  of  the  mountain  into  distinct  peaks,  uniformly  sur- 
rounded by  a  slope  of  rocks  or  fallen  earth.  Summits  of  this  kind 
are  being  formed  every  year.  In  some  localities  there  is  not  a 
single  green  bush  over  a  space  of  several  leagues  in  extent ;  the 
scanty,  gray-colored  pasturage  is  scarcely  visible  here  and  there  on 
the  slopes,  and  ruined  houses  blend  with  the  crumbling  rocks  that 
surround  them.  The  stream  in  the  valley  is  generally  nothing  but 
a  scanty  rill  of  water  winding  among  the  heaps  of  stones;  but  these 
very  heaps  of  shingle  and  rock  have  been  carried  down  by  the  tor- 

*  "  The  Earth,"  part  iii.  ch.  xlvii. 


520  THE   STORY  OF  OUR  PLANET. 

rent  itself  in  the  days  of  its  fury.  In  many  parts  of  its  course  the 
Haute  Durance,  which  is  generally  not  more  than  thirty  feet  wide, 
seems  lost  in  the  midst  of  an  immense  bed  of  stones  a  mile  and  a 
quarter  wide  from  bank  to  bank.  The  Mississippi  itself  does  not 
equal  it  in  dimensions. 

"The  devastating  action  of  the  streams  in  the  French  Alps  is  a 
very  curious  phenomenon  in  an  historical  point  of  view,  for  it 
explains  why  so  many  of  the  districts  of  Syria,  Greece,  Asia  Minor, 
Africa,  and  Spain  have  been  forsaken  by  their  inhabitants.  The 
men  have  disappeared  along  with  the  trees;  the  ax  of  the  wood- 
man, no  less  than  the  sword  of  the  conqueror,  have  put  an  end  to 
or  transplanted  entire  populations.  At  the  present  time  the  valleys 
of  the  Southern  Alps  are  becoming  more  and  more  deserted,  and 
the  precise  date  might  be  approximately  estimated  at  which  the 
departments  of  the  Upper  and  Lower  Alps  will  no  longer  have  any 
home-born  inhabitants.  During  the  three  centuries  that  have 
elapsed  between  1471  and  1776  the  vigncries  of  these  mountainous 
regions  have  lost  a  third,  a  half,  or  even  as  much  as  three-quarters 
of  their  cultivated  ground,  and  the  men  have  disappeared  from  the 
impoverished  soil  in  the  same  proportion.  From  1836  to  1866  the 
Upper  and  Lower  Alps  have  lost  25,090  inhabitants,  or  nearly  a 
tenth  of  their  population.  .  .  It  is  the  mountaineers  themselves 
who  have  made  and  are  seeking  to  extend  this  desert  which  sepa- 
rates the  valleys  of  the  Rhone  from  the  populous  plains  of  Pied- 
mont. If  some  modern  Attila,  traversing  the  Alps,  made  it  his 
business  to  desolate  these  valleys  forever,  the  first  thing  he  should 
do  would  be  to  encourage  the  inhabitants  in  their  senseless  work  of 
destruction.  Is  it  necessary  that  man  must  ultimately  rid  the 
mountains  of  his  odious  presence,  so  that  the  latter,  left  to  the  kind 
offices  of  beneficent  Nature,  may  again  some  day  recover  their 
forests  of  fir  trees  and  their  thick  carpet  of  flower-studded  turf?" 

The  statements  are  strong,  the  words  severe,  yet  they  are  hardly 
too  strong  or  too  severe.  In  parts  of  Europe  and  Asia  the  mischief 
which  has  been  wrought  by  the  reckless  destruction  of  the  forests, 
especially  in  the  mountain  regions,  is  almost  beyond  calculation ; 
parts  also  there  are  of  North  America  which  will  have  to  pay  the 
penalty  for  a  like  ill  doing.  Doubtless  in  many  cases  a  set-off  can 
be  pleaded ;  the  land  must  be  cleared  if  it  is  to  be  cultivated,  and 
the  cornfield  may  feed  more  mouths  than  the  forest ;  but  often  the 
work  of  destruction  has  been  so  selfish  and  reckless,  actuated  by 
the  lust  of  a  temporary  gain,  without  the  slightest  thought  of  the 


THE  DISTRIBUTION  AND    THE  DESCENT  OF  LIFE.  521 

effect  either  on  others  in  the  present  or  on  the  race  in  the  future, 
as  to  be  almost  inexcusable.  Not  seldom,  as  in  some  of  the  Ameri- 
can forest  fires,  the  mischief  is  the  outcome  of  that  savage  love  of 
destruction  which  it  would  be  a  misnomer  to  call  brutal  and  bestial, 
because  it  is  the  attribute  of  man  so  much  more  conspicuously  than 
of  the  animal  world. 

The  same  author  points  out,  in  another  place,*  that  climatal 
changes  also  result  from  the  cutting  down  of  trees.  By  that  the 
rainfall  undoubtedly  is  diminished,  and  this  may  be  a  serious  evil 
in  districts  where  it  is  already  light.  To  such  a  cause  the  present 
aridity  of  the  Sinaitic  peninsula  and  of  the  southern  parts  of  Pales- 
tine is  probaly  due.  In  the  days  of  the  Exodus  the  dry  plateau 
of  the  Tih  "must  have  borne  a  similar  relation  to  the  then  fertile 
region  of  the  Negeb  which  that  now  barren  tract  at  the  present 
day  bears  to  Palestine. "f  In  those  days  the  vine  was  cultivated 
freely  on  the  rocky  slopes  of  the  South  Country,  and  the  Land  of 
Promise  was  "a  land  of  brooks  of  water,  of  fountains  and  depths 
that  spring  out  of  valleys  and  hills."  Reclus  states;}:  that  the  clear- 
ing away  of  forests  "effects  a  change  in  the  network  of  isothermal, 
isotheral,  and  isochimenal  lines  which  pass  over  the  country.  In 
several  districts  of  Sweden  where  the  forests  have  been  recently  cut 
down,  the  springs  at  the  present  time  commence,  according  to 
Asbjiornsen,  about  fifteen  days  later  than  those  of  the  last  century. 
In  the  United  States  the  vast  clearings  which  have  been  made  on 
the  slopes  of  the  Alleghanies  appear  to  have  rendered  the  tempera- 
ture more  variable,  and  have  caused  autumn  to  encroach  upon  win- 
ter, and  winter  upon  spring.  Generally  speaking,  it  may  be  stated 
that  forests — which  in  this  respect  may  be  compared  to  the  sea — 
diminish  the  natural  differences  of  temperature  between  the  various 
seasons;  while  their  destruction  exposes  a  country  to  all  the 
extremes,  both  of  cold  and  of  heat,  and  adds  still  greater  violence 
to  the  atmospheric  currents." 

Evils  more  localized,  but  not  seldom  highly  pernicious,  arise  from 
industrial  processes,  such  as  mining  and  manufacturing,  and  even 
from  the  growth  of  cities.  There,  around  some  chemical  works, 
almost  for  miles,  vegetation  is  destroyed ;  there  the  land  is 
smothered  beneath  piles  of  rubbish,  whence  issue  foul  vapors  or 
fetid  smoke;  there  the  streams  are  polluted  with  the  waste 

*  "  The  Ocean,"  part  iii.  ch.  xxvii. 

f  Prof.  E.  H.  Palmer,  "  The  Desert  of  the  Exodus,"  part  ii.  ch.  iv. 

\  "  The  Ocean,"  part  iii.  ch.  xxvii. 


522  THE  STORY  OP  OUR  PLANET. 

products  of  factories  or  the  filth  of  sewage,  and  the  air  is  dense  with 
particles  of  carbon  and  sulphurous  vapors.  What  can  be  more 
unutterably  desolate  and  dreary  than  such  a  region  as  the  "Black 
Country"  of  South  Staffordshire,  or  the  environs  of  a  great  manu- 
facturing town,  such  as  one  of  those  in  Lancashire?  Even  the 
advance  of  a  so-called  "residential  quarter"  is  a  cheerless  sight;  for 
the  rigidity  of  dusty  roads,  however  well  made,  and  the  monotony 
of  streets  of  modern  villas,  even  if  not  "jerry-built,"  are  a  poor 
exchange  for  the  green  sward  and  the  shady  foliage  of  trees. 

Extenuating  circumstances  may,  no  doubt,  be  pleaded;  for  these 
plague  spots  on  the  face  of  Nature  are  often  the  sources  of  national 
prosperity.  But  a  little  care,  a  little  forethought,  a  little  self- 
restraint,  would  have  averted  many  of  the  greater  evils.  Man  has 
an  unlucky  habit — often  through  thoughtless  ignorance  or  sheer 
blundering — of  "making  the  worst  of  both  worlds,"  as  it  may  be 
called,  and  doing  much  mischief  in  general,  with  little  good  to  him- 
self in  particular.  Credit,  however,  may  be  claimed,  not  seldom, 
for  good  deeds.  If  the  earth  in  some  places  is  rendered  pestilential 
by  man,  in  others  it  is  made  more  healthy — malarious  marshes  have 
been  drained,  and  thus  fevers,  once  endemic,  have  been  mitigated 
or  have  disappeared.  Houses  are  beginning  to  be  built  on  the  low 
plain  of  the  Tuscan  Maremma,  and  the  peasants  no  longer  find  it 
always  necessary  to  retreat  each  night  from  their  work  to  the 
neighboring  hills.  Even  in  our  own  land  the  drainage  of  the  East 
Anglian  fens  has  made  ague  an  almost  unknown  disease,  and  has 
replaced  miles  of  waste  marsh  by  fertile  fields,  where  the  corn  in 
summer  "is  like  a  golden  ocean  becalmed  upon  the  plain."  By  the 
planting  of  trees  in  arid  lands  the  rainfall  has  been  increased,  and 
by  the  same  means  such  countries  as  those  which  have  been  already 
named  may  be  once  more  rendered  productive.  It  seems  inevita- 
ble that  in  the  progress  of  our  race  we  must  do  some  harm.  Rail- 
ways, steamships,  mines,  factories,  even  towns,  as  a  rule,  are  more 
or  less  of  eyesores  in  the  landscape.  All  that  is  beautiful — whether 
of  flowers  or  insects  or  birds — seems  to  vanish  from  before  the  face 
of  man,  in  much  the  same  way  as  the  feebler  races  of  his  own 
species  disappear  before  the  stronger.  Still  man  makes  waste 
places  fertile,  and  brings  distant  lands  into  closer  union ;  he  makes 
a  higher  civilization  possible,  and  gives  the  opportunity  for  wider 
knowledge  and  deeper  thought.  But  much  more  good  and  much 
less  harm  might  be  done.  When  wiser  counsels  prevail,  when  the 
lessons  learned  from  Nature  are  listened  to  by  statesmen  and  so- 


THE  DISTRIBUTION  AND    THE  DESCENT  OF  LIFE  523 

called  practical  men — then  a  better  day  may  dawn,  and  the  advance 
of  civilization  be  less  often  a  synonym  for  the  triumph  of  the  com- 
monplace, or  even  of  the  degrading.  Then,  perhaps,  a  reverence 
for  the  beauty  of  Nature  may  be  carried  so  far  that  the  worshipers 
of  Mammon  may  be  forbidden  to  mar*  its  fairest  scenes  with 
hideous  advertisements  of  the  fabrications  by  which  their  money 
bags  are  ;,lled,  or  nearly  to  poison  a  neighborhood  with  the  smoke 
and  vapors  of  their  factories. 

The  outlook  for  the  human  race  is  not  at  present  hopeful.  The 
reign  of  millennial  peace,  so  confidently  prophesied  forty  years  ago, 
seems  farther  off  than  ever,  and  the  destruction  of  European  civili- 
zation seems  rapidly  becoming  possible — not,  as  in  the  case  of  the 
Roman  Empire,  by  the  incursion  of  barbarian  races  from  without, 
but  by  the  eruption  of  the  savages  within  its  own  circle.  There 
was  some  hope  for  the  future  when  civilization  was  trampled  down 
by  a  horde  of  lusty  children  ;  but  what  is  there  when  it  is  destroyed 
by  its  own  waste  products?  The  teaching  of  Nature,  however,  is 
hopeful  on  the  whole,  though  it  is  not  always  so  for  the  individual, 
or  even  for  the  race.  The  long  annals  of  the  past  bear  testimony 
to  a  growth  and  a  development  which  are  so  conspicuous  that  we 
would  fain  hope  that  our  own  race  has  not  yet  reached  the  limit 
of  its  possibilities  or  the  measure  of  its  appointed  time;  for  the  his- 
tory of  the  earth  is  one  continuous  illustration  of  the  truth  of  the 
poet's  words: 

"  The  old  order  changeth,  yielding  place  to  new, 
And  God  fulfills  Himself  in  many  ways, 
Lest  one  good  custom  should  corrupt  the  world." 

*  An  oblong,  about  40  yards  square,  on  a  smooth  cliff  by  the  Devil's  Bridge  (Switzer- 
land) is  painted  red  and  inscribed  with  advertisements  (1893).  Above  it  is  a  pictur  of  the 
devil.  Very  appropriate  ! 


THE   END. 


GLOSSARY* 

of  a  few  geological  terms  in  this  book,  which  either  have  been  used  with- 
out explanation  or  may  be  readily  forgotten — Zoological  and  Botanical 
terms  not  included. 


Agglomerate. — A  name  often  given  to  the  fragmental  materials  ejected 
by  a  volcano  when  they  are  mostly  of  large  size  :  say,  from  as  big  as 
cricket  balls  upward. 

Augite. — A  mineral  which  is  a  silicate  of  magnesia,  lime,  and  iron  ; 
usually  green  or  dark  in  color. 

Basalt. — A  rock  of  igneous  origin,  dark  in  color  and  compact  in 
structure,  composed  chiefly  of  a  felspar,  augite,  some  iron  oxide,  and  often 
olivirie. 

Chert. — Differing  only  from  flint  in  being  rather  less  pure,  and  so  con- 
sisting mainly  of  silica,  much,  if  not  all  of  it,  in  a  crystalline  condition. 

Chlorite. — A  group  of  minerals  resembling  mica  in  general  habit ;  green 
in  color.  The  chief  constituents  are  silica,  magnesia,  iron,  alumina, 
water. 

Cipollino. — A  variety  of  marble  in  which  a  greenish  mineral  is  present, 
arranged  in  layers  more  or  less  wavy.  Thus  a  section  of  the  rock  has  an 
arrangement  like  the  coats  in  the  bulb  of  an  onion  (It.  cipolla),  whence 
the  name. 

Dolerite. — Closely  allied  to  basalt,  of  which  it  may  be  called  a  coarse- 
grained variety.  It  is  also  very  near  to  gabbro. 

Dolomite. — See  p.  152. 

Felspar. — A  group  of  minerals  differing  somewhat  in  form  and  com- 
position. All  are  silicates  of  alumina  ;  some  also  contain  potash  (this  is 
common  in  granite),  others  soda,  others  lime  or  lime  and  soda  (this  is 
common  in  basalt}. 

Felstone. — A  rock  of  igneous  origin,  compact  in  structure,  often  chem- 
ically identical  with  granite. 

Gabbro. — Composed  of  the  same  minerals  as  basalt,  and  differing  only 
in  that  it  is  coarsely  crystalline  and  contains  usually  a  special  variety  of 
augite,  which  has  a  "  platy  "  structure. 

Garnet. — A  very  varied  group  of  minerals,  the  commonest  being  wine- 

*A  word  printed  in  italics  in  an  explanation  will  be  found  elsewhere  in  the  Glossary. 

525 


526  GLOSSARY. 

red  ;  they  are  all  silicates  of  alumina,  and  among  other  possible  consti- 
tuents are  iron,  magnesia,  lime,  and  manganese. 

Glauconite. — A  mineral  chiefly  consisting  of  silica,  alumina,  iron,  potash, 
and  water. 

Gneiss. — A  rock  composed  of  the  same  minerals  as  granite,  but  exhibit- 
ing  a  certain  parallel  ordering  called  foliation.  (See  p.  291.) 

Granite. — A  rock  of  igneous  origin,  composed  of  crystalline  constituents, 
the  principal  being  quartz,  felspar,  mica. 

Graphite. — Mineral  carbon.     (The  familiar  "  blacklead  "  is  graphite.) 

Gypsum. — Sulphate  of  lime  combined  with  water,  and  in  a  crystalline 
condition,  occurring  in  masses. 

Hornblende. — A  mineral  which  is  a  silicate  of  magnesia,  lime,  and  iron  ; 
usually  green  or  dark  in  color  ;  chemically  identical  with,  but  mineralog- 
ically  distinct  from,  augite. 

Hydrous. — In  chemical  combination  with  water. 

Marble. — A  rock  formed,  properly  speaking,  wholly,  or  almost  wholly, 
of  crystalline  carbonate  of  lime,  differing  from  ordinary  limestone  in  that 
all  its  constituents  are  in  a  crystalline  condition  ;  but,  popularly,  the  word 
is  often  extended  to  include  any  limestone  which  will  take  a  polish. 

Mica. — A  group  of  minerals  of  "platy  "  habit,  with  a  metallic  luster  ; 
some  light,  some  dark  in  color.  The  chief  constituents  are  silica,  alumina, 
potash  or  soda  (sometimes  lithia),  and  in  one  group  iron  and  magnesia. 
The  "talc  "  of  commerce  is  a  mica. 

Obsidian. — A  glassy  rock  of  igneous  origin,  often  chemically  identical 
with  granite. 

Olivine. — A  mineral  which  is  a  silicate  of  magnesia  and  iron,  generally 
yellowish  or  somewhat  green  in  color. 

Peridotite. — See  p.  260. 

Pitchstone. — Nearly  the  same  as  obsidian. 

Pumice. — A  volcanic  rock  full  of  cavities  formed  by  steam,  commonly 
more  nearly  related  to  trachyte  than  to  basalt. 

Pyroxene. — A  name  generally  used  as  the  equivalent  of  augite,  but  which 
of  late  years  has  been  employed  in  a  wider  sense,  so  as  to  include  horn- 
blende and  one  or  two  closely  allied  minerals. 

Quartz. — The  usual  form  in  which  silica  (oxide  of  silicon)  crystallizes. 

Quartzite. — A  hard  rock  composed  of  grains  of  quartz  agglutinated 
together  so  that  they  are  sometimes  indistinct.  Probably  in  all  cases  it 
was  once  a  sandstone. 

Rock  salt. — Chloride  of  sodium  in  a  crystalline  condition,  occurring  in 
masses,  from  which  salt  (used  for  cooking,  etc.)  is  obtained. 

Schist.— A  crystalline  foliated  rock.  (See  p.  291.)  When  the  name 
of  a  mineral  is  prefixed,  this  indicates  that  the  mineral  is  abundant  in  the 
schist. 


GLOSSARY.  527 

Serpentine. — See  pp.  260  and  291. 

Silica. —  Oxide  of  silicon  ;  quartz  is  the  commonest  crystallized  form  ; 
opal  and  siliceous  sinter  are  colloid  varieties. 

Silicate. — Silica  in  chemical  combination  with  other  substances. 

Sill. — A  local  term  applied  to  sheets  of  igneous  rock,  when  they  have 
been  thrust  uniformly  between  strata,  like  a  card  between  the  leaves  of 
a  book. 

Staurolite. — A  silicate  of  alumina  and  iron,  dark  brown  in  color. 

Till. — A  glacial  deposit.  The  word  is  employed  by  some  as  equivalent 
to  bowlder  clay,  by  others  it  is  restricted  to  such  deposits  when  the 
materials  have  come  from  quite  near  at  hand. 

Trachyte. — A  volcanic  rock,  differing  from  felstone  in  being  yet  more 
compact,  and  even  glassy. 

Travertine. — A  rock  composed  of  carbonate  of  lime  precipitated  from 
water,  practically  identical  with  tufa. 

Tripoli.— See  p.  176. 

Tuff. — A  term  used  in  this  work  to  indicate  the  less  coarse  and  more 
distinctly  bedded  kinds  of  volcanic  ash  :  tufa  denoting  a  precipitate  of 
carbonate  of  lime  from  water. 


INDEX. 


Action,  Chemical,  of  Water,  93 
Aclour,  River,  Change  of  Mouth,  92 
Africa,  Physical  Features  and  Geology  of, 

421;  Rivers   of,  422-23  ;    Volcanoes   of, 

422 

Air,  Composition  of,  26 
Alpine  Lakes,  Formation  of,  137 
Alps,  History  of  the,  409-10  ;  Structure  of 

the,  211 

Alien  Fjord,  Raised  Beaches  in  the,  208-9 
America,     North,    Physical    Features    and 

Geology    of,  423  ;    Mountains   of,    424  ; 

Rivers  of,  425 
America,    South,     Physical    Features    and 

Geology    of,  426  ;  Mountains    of,  426  ; 

Post-Tertiary  Mammals  of,  475  ;  Rivers 

of,  427  ;  Volcanoes  of,  427 
Ammonites,  Variability  in  the  Genus,  435 
Amphibians,  The  First,  451  ;  Triassic,  453 
Animals,  Destructive  Effect  of,  172  ;  Per- 
sistent Forms  of,  432  ;  Recently  Extermi- 
nated, 431 

Anti-cyclones,  34,  36 
Apennines,  History  of  the,  411 
Aqueous  Vapor,  Action  on  Radiant  Heat, 

26 

Archaean  Era,  History  of  the,  335 
Archaean  Rocks,  Character  and  Significance 

°f>  351  I  in  Britain,  343  ;  in  Canada,  339; 

in  Europe,  345  ;  in  Scotland,  336 
Asia,  Mountain  Systems  of,  419  ;  Physical 

Features  and   Geology  of,    418  ;    Rivers 

of,  421 

Asiatic  Islands,  The,  421 
Atlantic   Ocean,    Submarine    Contours    of 

the,   51-54 

Atmosphere,  Pressure  of  the,  28 
Atolls,   189 
Australia, Fauna  and  Flora  of,  511  ;  Geology 

of,    427  ;    Post-Tertiary    Mammals    of, 

475  ;  Relation  of,  to  Other  Lands,  489 
Auvergne,  Lakes  of,    407  ;   Volcanoes    of, 

244 

Avalanches,  131 
Azores,  Fauna  and  Flora  of  the,  510 

B 

Ball,  Sir.  R.  S.,  on  Cause  of  Glacial  Epoch, 

498 
Baring-Gould,  Mr.  S.,  on  Iceland,  250 


Barometer,  Variations  of  the,  27 

Barrier  Reefs,  189 

Bars,  166  ;  and  Fresh-water  Pools,  166 

Basalt,  Columnar,  24,  287 

Beaches,  Raised,  160,  208,  401  ;  in  Britain, 

207  ;    in     Greenland,  205  ;    in  Norway, 

208  ;  in  Sweden,  206 

Bengal,  Bay  of,  Channel  in  the,  57 

Bermuda,  Advance  of  Sand  in,  89 

Birds,  Eocene,  Characteristics  of,  471 

Blocks,  Perched,  144 

"  Blowers"  and  Waves,  161 

Borings,  Deep,  in  Southeast  England,  380 

Botzen,  Earth  Pillars  near,  100 

Bowlder  Clay,  Distribution  and  Origin  of, 
393-96 

Breaks,  Stratigraphical  and  Palasontological, 
327 

Breezes,  Land  and  Sea,  33 

Bristol  Channel.  History  of  the,  398 

Britain,  Ancient  Physical  Geography  of, 
355-92  ;  Climate  of,  in  Glacial  Epoch, 
495  ;  Earthquakes  in,  265  ;  Significance 
of  Flora  and  Fauna,  508  ;  Later  Sculp- 
ture of,  398  ;  River  Courses  of,  398 

British  Fauna,  its  Relation  to  that  of  Europe, 
509  ;  Flora,  Peculiarities  of  the,  508 

Bunter  Group,  Physical  Geography  of  the, 
370  ;  Source  of  the  Pebbles  in  the,  371 


Calabria,  Earthquakes  in,  273 

Cambrian  Fauna,  441-42 

Cambrian  System,  Rocks  and  Geography 
of  the,  355 

Cambridge,  Whirlwind  near,  38 

Canons  and  Gorges,  109-10 

Cape  Breton,  Channel  in  Sea  Bed  near,  57 

Caraccas,  Earthquake  at,  271 

Carboniferous  Fauna,  448  ;  Flora,  439 

Carboniferous  System,  Rocks  and  Geog- 
raphy of  the,  361,  414 

Carclaze,  Rotten  Granite  at,  94 

Caspian  Sea,  Water  of  the,  50 

Caverns  Excavated  by  the  Sea,  160  ;  at  the 
Lizard,  162  ;  in  Arran,  163  ;  in  Sark, 
163 

Caves  in  Various  Localities,  103-4 

Chalk,  Absorptive  Properties  of,  93  ;  in 
Russia,  412  ;  Physical  History  of  the, 
385  ;  The  Red,  384 


53° 


INDEX. 


Change,    Epochs  of,  in   Certain   Families, 

etc.,  438 

Channels,  Submarine,  57 
Charleston,  Earthquake  at,  266 
Chemical  Changes  in  Rocks,  288 
Chili,  Earthquakes  in,  278 
Chronology,  Geological,  325 
Cirques  and  Conies,  106 
Cities,  Pernicious  Effects  of,  in  Nature,  521 
Clay,  Red,  in  Oceanic  Depths,  185  ;  Origin 

of,  187 

Cleavage,  Slaty,  24,  284 
Climate,  Causes  Affecting,  491  ;  in  Glacial 

Epoch,  493  ;  of    Past  Geological   Ages, 

497  ;  of  Tertiary  Era,  471 
Clouds,  Cause  of,  43  ;  Varieties  of,  44 
Coal  and  its  Structure,  179 
Coccoliths  and  Coccospheres,  183 
Colorado,  Canons  of,  1 10 
Concretions,  Formation  of,  174,  289 
Contemporaneity  of  Strata,  330 
Continents,  Grouping  of,  16 
Contorted  Rocks,  in  Alps,  etc.,  213 
Contours  of  Land  and  Sea  Bed,  53 
"  Coprolites,"  180 
Coral  Reefs,  189-96 
Corals,  The  First  Fossil,  444 
Corries  and  Cirques,  106 
Cotopaxi,  Eruptions  of,  234 
Crag,  The  Coralline  and  Red,  391-92 
Cretaceous  Fauna,  464  ;  Flora,  440 
Cretaceo'us  System,  Rocks  and  Geography 

of  the,  383,  412 
Crevasses  in  Glaciers,  78 
Crinoids,  Jurassic,  454 
Croll,  Dr.,  on  Cause  of  Glacial  Epoch,  498  ; 

on  Motion  of  Glaciers,  76 
Cromer,  Glacial  Deposits  at,  393  ;  Pliocene 

Deposits  at,  392 
Crust,    Internal   Changes   in    the    Earth's, 

284-93 
Currents,  Aerial,  29  ;  Marine,  Produced  by 

Changes  of  Temperature,  67  ;  Produced 

by  Influx  of  Rivers  into  the  Sea,  67 
Cutch,  Runn  of,  Changes  of  Level  in,  204, 

276 
Cyclones,  34,  37,  40  ;  Causes  of,  41  ;  Paths 

of,  41 


Dana,  Professor}.  D.,  on  Kilauea,  226  ;  on 
Sandwich  Islands,  224 

Darwin,  Charles,  his  Theory  of  Coral  Reefs, 
190 ;  Disputes  Regarding,  191  ;  on  the 
Work  of  Earth  Worms,  173 

Darwin,  Professor  G.,  on  Precessional 
Movement,  315 

Daubre'e,  Professor,  Experiments  on  Con- 
tracting Balls,  309 ;  on  Glass,  290 

Davison,  Mr.  C.,  Strain  Zone  in  Earth's 
Crust,  316 

Davy,  Sir  H.,  Theory  of  Regarding  Vol- 
canoes, 256 


Dead  Sea,  The,  153  ;  Evaporation  from,  66  ; 
Water  of,  50 

De  Charpentier,  M.,  on  Motion  of  Gla- 
ciers, 75 

Dee  (Flint),  Estuary  of,  154  ;  Valley 
of,  400 

Dee  (Scotch),  Water  in,  120 

Delta  at  Rivington  Waterworks,  124  ;  of 
the  Mississippi,  169 ;  of  the  Nile,  124  ; 
of  the  Po,  170;  of  the  Rhine,  123;  of 
the  Rhone,  169 

Derbyshire,  Caves  of,  103 

De  Saussure  on  Motion  of  Glaciers,  74 

Devonian  Fauna,  447  ;  Flora,  438 

Devonian  System,  Rocks  and  Geography  of 
the,  359 

Dinosaurs,  Carnivorous,  461  ;  Certain 
Forms  of,  Described,  460  ;  Herbivorous, 
466  ;  Relation  to  Birds,  462 

Dolinas,  104 

Dolomite  and  Coral  Reefs,  414 

Dunes,  Advance  of,  89  ;  and  Eccles  Church, 
89  ;  Formation  of,  86  ;  Magnitude  and 
Shape  of,  87  ;  of  Gascony,  92  ;  Stratifica- 
tion of,  91 

Dust  and  After  Glows,  92  ;  Transport  of, 
by  Wind,  91 

Dutton,  Captain  E.,  on  Charleston  Earth- 
quake, 266 


Earth,  Condition  of  its  Interior,  311  ;  Con- 
ditions of  First  Consolidation  of,  307-10  ; 
Connection  between  Temperature  and 
Age  of,  482  ;  Density  of  its  Interior,  313; 
Form  of,  8  ;  Internal  Condition  of,  309, 
311,  314;  Precession  of  its  Axis,  314; 
its  Beginning,  298,  303,  306  ;  its  Crust, 
Rate  of  Increase  of  Temperature  in  Early 
Times,  352  ;  Movements :  Post-Ordo- 
vician,  357  ;  Post-Silurian,  359  ,  362  ; 
Devonian,  362  ;  Post-Carboniferous,  386  ; 
Post-Permian,  370  ;  Post-Cretaceous,  386, 
389,  400,  410,  415  ;  Orbit  and  Velocity 
of,  8  ;  Changes  in  its  Movement,  417  ; 
Supposed  Age  of,  481  ;  Temperature  of 
First  Crust,  307  ;  Temperature  of  its 
Interior,  311  ;  Thickness  of  Crust  of, 
314 

Earth  Pillars,  Formation  and  Localities  of, 
99-102 

Earthquakes  and  Change  of  Level,  276  ; 
and  their  Effects,  262-83  \  Causes  of, 
281  ;  in  Britain,  265  ;  in  Calabria,  273  ; 
in  Caraccas,  271  ;  in  Chili,  278  ;  in  Is- 
chia,  271  ;  in  Japan,  269  ;  in  Lisbon,  272  ; 
in  Runn  of  Cutch,  276  ;  in  South  Caro- 
lina, 266  ;  Periodicity  of,  281  ;  Spread 
and  Emergence  of  Shock,  263 ;  Velocity 
of  Wave,  266,  269,  279 

Earth  Worm,  The,  a  Geological  Agent,  173 

Eccentricity  of  Earth's  Orbit,  Effect  of 
Changes  in,  503 


INDEX. 


53' 


Eccles  Church  an*  Sand  Hills,  89 

Kchinoids,  First,  446 

Ecliptic,  Effect  of  Oscillations  on  Obliquity 

of,  502 

Eifel,  Craters  in  the,  246 
Eigg,  Scuir  of,  its  History,  390 
Eocene    Birds,    their    Peculiarities,    471  ; 

Flora,  441 
Eocene  System,    Rocks  and  Geography  of 

the,  386,  410 

Eozoon  Canadense,  Description  of,  347 
Erosion,  Subterranean,  97 
Escarpments,  Formation  of,  114 
Essex,    Buried    River    Channel    in,    396, 

Earthquake  in,  265 
Estuaries,  Silting  up  of,  166 
Europe,  Ancient  Glaciers  of,   406  ;    Chief 

Physical  Features  of,   405  ;    Mountains, 

Genesis   of   the,  408  ;    their   Age,    417; 

Rivers  of,  418 
Evans,   Sir  J.,  on  Possible  Cause  of  Cli- 

matal  Change,  497 

Evaporation,  43,  45  ;  by  Solar  Heat,  66 
Evolution,  Remarks  on,  505 
Explosion,  Effects  of,  282 


False  Bedding,  22 

Faults,  Amount  of  Displacement  Caused  by, 
286  ;  Overthrust,  214  ;  Various,  285 

Fauna,  Cambrian,  441-43  ;  Carboniferous, 
449  ;  Changes  in  a,  Significance  of,  327  ; 
Cretaceous,  464  ;  Devonian,  447  ;  Ju- 
rassic, 454  ;  Neocomian,  464;  Ordovician, 
443  ;  Permian,  45 1  ;  Silurian,  445  ;  Tri- 
assic,  453 

Filtration  through  Chalk  and  Sand,  93 

Fisher,  Mr.  O.,  on  the  Interior  of  the 
Earth,  317 

Fishes,  The  First,  447 

Flints,  Residual,  above  and  below  Ground, 
97  ;  Worked  by  Primeval  Man,  320 

Floods,  125  ;  at  Cambridge,  125  ;  at  Tou- 
louse, 125  ;  in  the  Ziller-thal,  126  ;  of  the 
Garonne,  125 

Flora,  Carboniferous,  439  ;  Devonian,  438; 
Eocene,  441  ;  First  Indubitable  Traces 
of,  438  ;  Fossil,  Sketch  of,  438  ;  Ju- 
rassic, 440  ;  Neocomian,  440  ;  Ordovician, 
438  ;  Permian,  440  ;  Secondary  and  Ter- 
tiary, 440  ;  Silurian,  438  ;  Triassic,  440 

Fog,  Mist,  and  Cloud,  44 

Folds  in  Rocks,  213,  284 

Foliation,  Definition  and  Cause  of,  291 

Foraminifera  as  Rock  Builders,  180 

Forbes,  Professor  J.  D.,  on  Motion  of  Gla- 
ciers, 74 

Forests,  Results  of  Destruction  of,  519 

Fossils,  Definition  of,  319  ;  Obliteration  of , 
by  Heat,  291  ;  The  First  Traces  of,  346  ; 
The  Lessons  of,  3 

Fringing  Reefs,  189 

Fucoids  in  the  Older  Rocks,  438 


Gaping  Gill  and  Ingleborough  Caves,  102 

Gault,  Variation  in  the,  384 

Geikie,  Sir  A.,  on  Scuir  of  Eigg,  390 

Geological  Record,  Imperfections  of  the, 
332 

Geysers,  Eruptions  of,  Explained,  249-53  ; 
in  Iceland  and  Yellowstone,  250 

"Giants'  Kettles,"  133 

Glacial  Deposits,  Accounts  of,  393—96 

Glacial  Epoch,  Climate  of,  493  ;  Distance  of, 
from  Present  Time,  505  ;  Possible  Causes 
of,  498 

Glaciers,  Ancient  Extent  of,  135  ;  Connec- 
tion with  Lake  Basins,  1 36  ;  Crevasses  of, 
77 ;  Effects  of,  133-35  ;  Formation  of, 

»  69  ;  History  of,  131  ;  Motion  of,  and  its 
Cause,  71-76  ;  Oscillations  of  Alpine,  73  ; 
Rate  of  Motion  of,  73  ;  Glacier  Tables, 
144  ;  Transporting  Effect  of,  142-51 

Glauconite,  Formation  of,  in  Sea,  187 

Globigerina,  182 

Gloppa,  Shell-bearing  Gravels  at,  396 

Gorges  and  Canons,  109-10 

Graham  Island,  Eruption  of,  238 

Granite  Rotted  by  Water,  94  ;  Granite 
Tors,  95 

Graptolites,  443 

Green,  Professor  A.  H.,  on  Genesis  of  Solar 
System,  305 

Greenland,  Sinking  of  Land  in,  205 

Greensand,  Lower,  Variation  in  the,  383  ; 
Upper,  Variation  in  the,  384 

Guano,  180 

Gulf  Stream,  63 

H 

Heat  and  Water,  Effects  on   Rocks,  290  ; 

Radiant  Heat  and  Aqueous  Vapor,  26 
Hebridean  Rocks,  337 
Heilprin,  Professor,  Estimate  of  Thickness 

of  Stratified  Rocks,  329 
Heim,    Dr.,    on    Quantity   of    Mud    from 

Glaciers,  147 

Hindustan,  Geology  of,  418 
"  Homotaxis,"  332 
Hopkins,  Mr.,  on  Motion  of  Glaciers,  74; 

on  Thickness  of  Earth's  Crust,  314 
Horse,  Pedigree  of  the,  516 
"  Horst,"  Description  and  Discussion  of  a, 

218 

Huronian  System,  339,  343 
Hurricanes,  38-43 
Huxley,  Professor,  on  Contemporaneity  and 

Homotaxis,  330-32 

I 

Ice,  Crystals  of,  69  ;  Expansive  Action  of, 
129 

Icebergs,  Foot  and  Floe,  151,  395  ;  Forma- 
tion of,  149  ;  on  River  Beds,  151  ;  Trans- 
port by,  150 


532 


INDEX. 


Ice  Cap,  Folar,  Supposed  Effect  of,  on  Sea 
Level,  207 

Iceland,  Geysers  of,  250 ;  Volcanic  Erup- 
tions in,  248 

Ice  Sheets,  149,  394,  406 

Igneous  Rocks,  Mode  of  Occurrence  of, 
259  ;  Origin  of,  257-61 

Iguanodons,  Cemetery  of,  in  Belgium,  466 

Indian  Ocean,  Submarine  Contours  of  the, 
55 

Ingleborough,  Caves  near,  102 

Insects,  Fossil,  in  Carboniferous  System, 
450 

Interglacial  Ages,  502 

Ischia,  Earthquakes  in,  271 

Isotherms,  Course  of,  in  Northern  Hemi- 
sphere, 493 


Japan,  Earthquakes  in,  269  ;   Eruption   of 

Bandai-san,  231 

ointing,  Prismatic  or  Columnar,  24,  287 
oints  and  Weathering,  96 
oint  Structures,  23,  286 
udd,  Professor,  on  Krakatoa,  231 
ura,  Structure  of  the,  211 
urassic  Beds  in  Scotland,  381 
urassic    Fauna,  454  ;    Flora,    440 ;    Mol- 

luscan    Fauna,    Characteristics   of,   457  ; 

Vertebrata,  457 
Jurassic  System,  Rocks  and  Geography  of 

the,  377,  413 

K 

Kelvin,  Lord,  on  Condition  of  Earth's  In- 
terior, 313-15  ;  on  Former  Crust  Tem- 
perature, 352 

Keuper  Group,  Physical  Geography  of,  314 
Khasia,  Ghauts,  Rainfall  of  the,  47 
Kilauea,  Crater  of,  225,  306  ;  Subterranean 

Course  of  Lava  from,  242 
Krakatoa,  Eruption  of,  226 


Lake  Basins,  136 

Lakes,  Alpine,  136  ;  North  American,  140 

Lamination,  21 

Land  and  Sea,  Distribution  of,  16  ;  below 
Sea  Level,  15  ;  Surface  of  the,  12 

Landslips,  126  ;  at  Evionnaz,  126  ;  at 
Lyme  Regis,  127  ;  of  the  Rossberg,  127  ; 
of  the  Undercliff,  126 

Lauren tian  Rocks,  339 

Lava,  Constructive  Effects  of,  176  ;  Dis- 
charge of,  241  ;  Temperature  of,  243 

Lava  Stream,  Aspect  of  a,  243  ;  Explosion 
in  a,  249 

Lenham,  Pliocene  Deposits  at,  392 

Level,  Changes  of,  in  Earth's  Crust,  199- 
210  ;  of  Sea  and  Ice  Caps,  207 

Lias,  Physical  Geography  of  the,  378 

Life,  Distribution  of,  on  the  Globe,  508 


Lignite,  179  • 

Limestone,    Crystalline,    Origin    of,    342, 

346  ;     Recent,     from     Mollusks,     188  ; 

Weathering  of,  104 
Lisbon,  Earthquake  at,  272 
London  Clay,  Physical  History  of  the,  387 
Lucrine  Lake,  223 

M 

Madagascar,  Extinct  Birds  of,  476  ;  Rela- 
tion of  Fauna  to  that  of  Africa,  488 

Mallet,  Mr.,  on  Calabrian  Earthquakes, 
274  ;  Theory  of,  Regarding  Volcanic 
Action,  257 

Mammals,  Eocene  and  Miocene,  472  ; 
Pliocene,  473  ;  Post-Tertiary,  474  ;  The 
First,  453 

Mammoth  Caves,  Kentucky,  105  ;  Portrait 
of  the,  475 

Man  and  Extinct  Mammals,  475  ;  his 
Effects  on  Nature,  578  ;  his  Wanton 
Injuries  to  Nature,  522 

Manganese,  Nodules  of,  185 

Masamarhu  Island,  195 

Mediterranean  Sea,  Submarine  Contours 
of,  56 

Medway,  Valley  of  the,  115 

Mendip  Hills,  103 

Merostomata,  Fossil,  445 

Metamorphism,  21,  288,  291 

Meteors,  Composition  of,  299 ;  Path  of, 
300 

Meuse,  Windings  and  Valley  of  the,  112 

Milne,  Professor  J.,  Observations  on  Earth- 
quakes, 269,  282 

Mineral  Springs,  98,  116-18;  Veins,  His- 
tory of,  292 

Miocene   Mammals,  472 

Miocene  System,  Rocks  and  Geography  of 
the,  389,  406 

Mississippi,  Delta  of  the,  169 

Mist,  Fog,  and  Cloud,  44 

Moel  Tryfan,  Shell-bearing  Gravels  at,  396 

Mollusks  and  Limestone,  188,  195 

Monsoons,  32 

Monte  Nuovo,  Eruption  of,  223 

Moraine  Profonde,  145,  394 

Moraines,  142 

Moseley,  Canon,  on  Motion  of  Glaciers,  75 

Mountain  Chains,  Relation  of,  to  Oceans, 
17  ;  Descriptions  of  Various,  15  ;  Systems 
of  Asia,  419  ;  of  America,  424,  426  ;  of 
Europe,  408 

Mountains  and  Folded  Rocks,  214  ;  At- 
mospheric Pressure  on  Summits  of,  28 

Mud  from  Glaciers,  147,  393 

Muschelkalk,  413 

N 

Nebulrc,  Composition  of  the,  302 
Neocomian  Fauna,  464  ;  Flora,  440 
Neocomian  System,  Rocks  and  Geography 
of  the,  382,  413 


INDEX. 


533 


New  Zealand,  Changes  of   Level   in,  204  ; 

Extinct  Birds  of,  476  ;  Physical  Features 

and     Geology     of,    428 ;    Post-Tertiary 

Mammals,  476 
Nile,  Delta  of  the,  170 
Nomenclature,  Geological,  322 
Norian  Rocks,  339 

Norman,  Mr.,  on  Volcano  in  Japan,  231 
North  America,  Whirlwinds  in,  39 
Norway,  Channel  off  Coast  of,  57  ;  Raised 

Beaches  in,  2oS 


Ocean,  Currents  of ,  62  ;  its  Work,  152-71  ; 

Oceans     and     Mountain    Chains,      17  ; 

Oceans,  Grouping  of,  17 
Ocean  Basin,  Permanence  of,  486 
Old   Red  Sandstone,   Physical   History   of 

the,  360 

Olenellus,  Discovery  of,  in  Northwest  High- 
lands, 355 
Oligocene  System,  Rocks  and  Geography  of 

the,  388,  408 
Oolites,  Physical  Geography  of  the  Lower, 

378  ;  Middle,  379  ;  Upper,  379 
Ordovician  Fauna,  443  ;  Flora,  438 
Ordovician  System,  Rocks  and  Geography 

of  the,  356 

Organisms  and  Rock  Formation,  175-76 
Overlap,  Definition  of,  327 


Pacific  Ocean,  Submarine  Contours  of  the, 

Palaeozoic  Fauna,  Summary  of  the,  452 
Palestine,  Former  Condition  of,  521 
Peak  Cavern,  103 
Peat   and   its   Growth,    177  ;     in    Various 

Countries,  178 

Pennine  Range,  Age  of  the,  368 
"  Perched  Blocks,"  145 
Permian  Fauna,  451  ;  Flora,  440 
Permian  System,  Rocks  and  Geography  of 

the,  367,  414 

Pfafers,  Gorge  of  the  Tamina  at,  108,  109 
Phlegrsean  Fields,  Craters  of  the,  223 
Plants  as  Rock   Makers,   176 ;    Geological 

Effect  of,  172  ;  Protective  Effects  of,  173 
Plateau,  M.,  Experiment  by,  305 
Pliocene  Mammals,  473 
Pliocene  System,  Rocks  and  Geography  of 

the,  391,  406 
Po,  Delta  of  the,'i68 
Poik,  Subterranean  Course  of  the,  104 
Port  Kennedy,  Rise  of  Land  at,  206 
Post-Tertiary  Mammals,   474 ;    Vertebrata 

in  Southern  Hemisphere,  475 
Pozzuoli,    Eruption   near,    223  ;    Rise   and 

Fall  of  Land  near,  200 
Precession,  Effect  of,  on  Climate,  501 
Precession  of  Earth's  Axis,  315  ;  its  Rela- 
tion to  Solidity  of  Interior,  314 
Pressure  and  Vulcanicity,  257  ;  Effects  of, 


•  in  Altering  Rocks,  290 ;  of  the  At- 
mosphere, 28 

Prestwich,  Professor,  on  Lenham,  391  ;  on 
Thames  Valley,  397 

Primary  Era,  Earlier  Geology  of  the,  in 
Europe,  417 

Pterodactyles,  462 

Pyrenees,  History  of  the,  411 


Radiolaria,  183 

Rain,  Action  of,  on  Rock  Surfaces,  94  ; 
Cause  of,  43  ;  Sculpturing  Action  of, 

93-9-6 

Rainfall.  British,  46  ;  in  Certain  Districts, 
45-48  ;  in  the  Khasia  Ghauts,  48  ;  Laws 
of,  45 

Rainless  Regions,  48 

Rain  Prints,  Fossil,  99 

Ramsay,  Sir  A.,  on  Excavation  of  Lake 
Basins,  136 

Ravenna,  and  the  Delta  of  the  Po,  168 

Reade,  Mr.,  on  Mountain  Making,  216 

Reclus,  on  Destruction  of  Forests  in  Dau- 
phine,  519 

Red  Clay,  Oceanic,  Formation  of,  185  ; 
Origin  of,  187 

Red  Sea,  Evaporation  from  the,  67 

Reefs,  Connection  with  Atolls,  190  ;  Fring- 
ing and  Barrier,  189 

Repetition,  Absence  of,  in  Living  Crea- 
tures, 436 

Reptiles,  Flying,  462  ;  of  Jurassic  Times, 
458  ;  The  First,  452 

Reuss,  Valley  of  the,  214 

Rhaetic  Beds,  their  Significance,  377 

Rhone,  Delta  of  the,  169 

Rivers,  Mineral  Salts  in,  119-21  ;  of  Africa, 
422  ;  of  America,  North,  425  ;  of  Amer- 
ica, South,  427  ;  of  Asia,  421  ;  of  Europe, 
418  ;  Power  of  Transporting  Materials, 
120-25  ;  their  Flow  and  their  Banks, 
110-13  I  Windings  of,  108,  112 

Roches  Moutonnees,  134 

Rocks  and  Rain  Action,  94  ;  Aqueous  and 
Igneous,  19  ;  Changes  in  Nature  of,  21  ; 
Effects  of  Changes  of  Temperature  on, 
84  ;  Various  Kinds  of,  19 ;  Worn  and 
Polished  by  Sand,  85 

Roslyn  Hill  (Ely),  Bowlder  at,  393 


St.  George's  Channel,  History  of,  399 
Salt,  Amount  of,  in  Sea,  152 
Salt  Lake  in  Triassic  Times,  375 
Salt  Lake,  the  Great,  153  ;  Water  of,  50 
Sand,  Absorptive  Properties  of,  94  ;  Effect 
of  Wind  on  Grains  of,  85  ;  Sand  Pipes, 
97  ;  Solidification  of,  91  ;  Traveling  of, 
87-90 

Sandwich    Islands,   Borings   in,   195  ;  Vol- 
canoes of,  224,  242,  248 
Scandinavia,  Changes  of  Level  in,  205 


534 


INDEX. 


Schists,  Age  of  the  Crystalline,  339  ;  Al- 
leged Jurassic,  Age  of,  341  ;  Alleged 
Lower  Silurian,  Age  of,  344  ;  Definition 
of,  291  ;  Origin  of,  391 

Scotland,  Ancient  Volcanoes  of,  246,  248 

Sea,  Contours  of  Bed  of,  53,  58  ;  Encroach- 
ments of,  157  ;  at  Dunwich,  158  ;  at 
Reculver,  158  ;  in  Norfolk,  157 ;  in 
Yorkshire,  157  ;  on  South  Coast,  159  ; 
Inland,  Composition  of  Waters  of,  51  ; 
Sea  Serpents,  Extinct,  465  ;  Supposed 
Change  of  Level  of,  Discussed,  207  ;  The 
Dead,  153 ;  Sea  Water,  Composition 
of,  50 

Secondary  Era,  Summary  of  Life  History 
of  the,  468 

Sediments,  Supposed  Melting  of,  260 

Septarian  Stones,  174 

"  Serapis,  Temple  of,"  as  Evidence  of 
Change  of  Level,  201 

Severn,  Valley  of  the,  398 

Shasta,  Mount,  Earth  Pillars  near,  102 

Silurian  Fauna,  445  ;  Flora,  438 

Silurian  System,  Rocks  and  Geography  of 
the,  358 

Skapter  Jokul,  Eruption  of,  248 

Skye,  Volcanic  Rocks  in,  390 

Slaty  Cleavage,  24 

Snow  and  Ice,  68  ;  Formation  of,  130 

Snow  Line,  The,  70 

Soil,  Formation  of,  96 

Solar  System,  9  ;  its  Beginning,  303-5 

Solent,  Valley  of  the,  401 

Specialization,  Results  of  Excessive,  468 

Spheroidal  Structure  in  Rocks,  288 

Sponges,  Siliceous,  183 

Springs,  Mineral,  98,  116-18 

Stars,  Composition  of  the,  362 

Steinerne  Meer,  The,  104 

Strata,  The  Order  of,  6 

Stratification,  21 

Stratified  Rocks,  Names  for  Groups  of, 
324  ;  Thickness  of,  329 

Stratigraphical  Classification,  Principles  of, 
326-28,  330 

Streams,  Velocity  and  Curvature  of,  108, 
110-13 

Stromatoporids,  446 

Submarine  Geography,  52-58 

Submerged  Forests,  401  ;  Valleys,  402 

Sun,  Composition  and  Condition  of  the, 
300  ;  Probable  Age  of  the,  484 

Swallow  Moles,  103 

"  Swatch  of  No  Ground,"  The,  57 


of  the,  469  ;  Mollusca,  Progressive 
Changes  in  the,  470  ;  Peculiar  Forms,  471 

Thames,  History  of  Valley  of  the,  397  ; 
Mineral  Matter  in  the,  120 

Thibet,  Plateau  of,  421 

Tides  and  their  Effects,  59,  154  ;  at  Lowes- 
toft,  62 ;  Effects  of,  on  Earth's  Rota- 
tion, 482  ;  in  Mediterranean,  60  ;  in  the 
Wye  and  Avon,  62  ;  on  the  British 
Coast,  62 

Time,  Geological,  Comparative  Length  of 
Subdivisions  in,  329  ;  Duration  of,  328 

Tornado,  38-43 

Torridan  Sandstone,  337,  343 

Trade  Winds,  29 

Trees,  Effects  of,  on  Rainfall,  521 

Trent,  Valley  of  the,  401 

Triassic  Fauna,  452  ;  Flora,  440 

Triassic  System,  Rocks  and  Geography  of 
the,  370,  413 

Trigonia,  456 

Trilobites,  442 

Tyndall,  Professor,  on  Motion  of  Glaciers. 
74 

Typhoon, 38-43 

Tyrol,  Whirlwind  in  Italian,  38 

U 

Uddevalla,  Rise  of  Land  at,  206 
Unconformity,  Definition  of,  327 


Valleys  and  Rock  Structure,  109-12,  114  ; 
Formed  by  Erosion,  105-15  ;  Forms  of, 
105-13  ;  Heads  of,  106-7  ;  Terraced 
Walls  of,  114 

Vapor,  Aqueous,  the  Action  of,  26 

Variability,  Results  of,  Sometimes  Destruc- 
tive, 436 

Veins,  Mineral,  History  of,  292 

Vesuvius,  Eruptions  of,  236 

Vitality,  Exhaustion  of,  517 

Volcanic  Dust,  Traveling  of,  92,  229,  236 

Volcanic  Eruptions  and  Action  of  Steam, 
255  ;  and  Crushing  of  Rocks,  256 

Volcanic  Rocks  of  Carboniferous  Period, 
369 ;  of  Devonian,  361  ;  of  Ordovician, 
356  ;  of  Permian,  369,  415  ;  of  Silurian, 
358  ;  of  Tertiary,  389,  407,  408 

Volcanoes,  Description  and  Effects  of, 
220-55  ;  Geographical  Distribution  of, 

253  ;  Position  of,  in  Regard  to  the  Sea, 

254  ;  Structure  of,  243  ;  Submarine,  239 


Temperature  of  Earth's  Crust,  Former 
More  Rapid  Increase  of,  352  ;  Differ- 
ences of,  131 

Tertiary  Era,  Physical  Geography  of  the, 
386-406  ;  Fauna,  Summary  of  Character- 
istics of  the,  469  ;  Mammals,  Incoming 


W 

Water,  Chemical  Action  of,  93-98,  116-20; 

Mechanical  Effects  of,  99,  121-25 
Waterfalls,  Formation  of,  106 
Waves,  Depth  at  which  they  are  Felt,  165  ; 

Fissures  and  Caverns,  159-64  ;  Force  and 

Effects    of,    155-66  ;    Earthquakes    and 

Sea,  230,  272,  276 


INDEX.  535 

Weald,  Denudation  of  the,  115;    Physical  Winds    and      Barometric     Pressure,      34; 

History  of  the,  382  ;  in  Germany,  413  Causes   of,    29  ;  Local,  33  ;    the  Trades 

Weathering  and   Joint   Structures,   95  ;  of  and  Counter  Trades,  29 

Rocks,  94-96,  104  Wind-worn  Rocks,  85 

Wells,  Springs  near  Cathedral  of,  103  Wookey  Hole,  103 
Whirlwinds,  38-43 

Whymper,   Mr.  E.,   on  Eruption  of  Goto-  Y 

paxi,  235 

Windings  of  Rivers,  108,  110-12  Yellowstone,  Geysers  of  the,  250 


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